As established elsewhere, amnesia comes up a lot in TV. Amnesia is a funny thing in the real world and can give you lots of strange symptoms.
In TV, it's very weird too, but it's much more specific. Amnesia has several basic attributes in TV land:
1. With surgical precision, amnesia strips you of all information pertaining to personal identity, leaving just about everything else intact. TV Amnesia is a disorder where you forget where you put your keys, but you do not forget what a key is or what it's for. You will forget where you went to school, but not any of the things you learned in school. As a result, the character will retain all of their skills — though they may not know they have them at first.
Interestingly, while this would seem to be Hollywood Science at first glance, this really is how retrograde amnesia works (well, some of the time). "Procedural memory," which governs skills that the brain has automated, appears to be separate from "declarative memory", where you store previous facts and events, and in many cases only one of the two is damaged. And then there's muscle memory, which may or may not be affected by amnesia.
2. In a series with Plausible Deniability, amnesia typically also erases all knowledge of the Masquerade. The character will completely forget that aliens, monsters, vampires and such are real, but will remember that normal people don't believe in such things. This can seem especially odd if that's the sort of thing the character never believed in the first place: if you don't remember anything, how do you know that aliens and werewolves are any stranger than the sun coming up in the morning and setting at night? Even more odd if the character is himself an alien or supernatural being and subsequently "defaults to Muggle" after losing his memory. Occasionally, this is paired with Fake Memories to create an elaborate deception.
3. With very few exceptions, amnesia is always entirely retrograde: memory loss extends backward from the moment of injury. Anterograde amnesia (the inability to accumulate new memories) has only started to come up in recent years, usually in comedies. Amnesia usually extends back clean to birth. Real amnesia resulting from head trauma or drugs is usually confined to a short period on both sides (before and after) of the incident.
4. If a tool of the group the protagonists belong to, the likelihood of abuse of this power is almost never addressed. There's little interest, procedure, or group devoted to making sure someone isn't stealing from, raping, killing or committing other crimes against Muggles and then erasing their memory of it. After all, who cares about Muggles as long as the Masquerade is intact?
Very useful in maintaining that things are No Big Deal. To this end, it's pretty standard for The Men In Black to use this on anyone who's seen too much, often employing a Memory Wiping Crew. Contrast Exposition Beam. Can cause an Amnesiac Hero to be born.
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In Pandora Hearts, this is played straight for many of the characters. Gil wishes to know who his master really is, Alice wants to regain her memories of her life before she became a chain, and Oz wants to discover the truth behind his sin. The results are very, verydisturbing. Where shall we begin?
Ah, the heroine, Alice the Bloody Black Rabbit, a rough girl who used to be a human until her best friend, a stuffed rabbit named Oz, came to life and was used as a tool of destruction against his will. She killed herself to end his suffering and then her soul took over his body, stealing his power, wiping her memories and her sister's in the process.
Gilbert, Oz's little servant who used to be Jack's servant Actually, he was Glen's servant, and he acquired amnesia via being STABBED in the back by Jack. [[spoiler:Oz is an Artificial Human whose true form is an Animate Inanimate Object; a stuffed plush rabbit that came to life and wound up in his contractor's body that was deaging and believed himself to be human. He lost all his memories of being B-rabbit somehow-the manga hasn't explained that yet.
Also, Elliot lost his memories of killing his own family with Humpty Dumpty's help.
Masane Amaha in Witch Blade plays this straight with #3 (classic trauma induced amnesia), but this is subverted later when she never gets her memories back.
Strawberry Panic: Amane falls from her horse and forgets that she was going to enter the Etoile election, and her relationship with Hikari. She remembers having been asked to enter, and the rest of the details of her life. (This is surprisingly similar to the post trauma memory loss that is actually but rarely incurred by some people.)
In The Big O, a major part of the original plot is that everyone in Paradigm City — and apparently whatever is left of the world, as well — has amnesia of unknown origin. Unable to recall who they were before the incident (but still retaining most of their day-to-day survival skills), everyone begins life anew. Then odd and disturbing reminders start appearing, many years later... The finale implies that they're all characters in an anime series.
A Wind Named Amnesia deals with the whole world suffering from sudden amnesia and not a pretty type: people were turned down to almost animal behaviour while only the main protagonist was restored to humanity by psionics and training.
Bleach has a similar memory erasing plot device, with the downside that the blank is generally filled in by something random from the person's imagination. It has fun with what the blanks are filled with, such as a particularly strange character who "remembers" that the reason there is a hole in the classroom and a missing student is because an army of monkeys burst into class and dragged him away.
They later gain an upgraded version without that particular problem, but by this time half the cast has some level of spirit power, and thus the memory modification fails to one degree or another on them.
The third movie has villains that can perform a different method that erases entire characters from others' memories. It's surprisingly through to the point where a character who trained like mad to get strong enough to save an erased character forgets his training and thinks he's much weaker than he actually is. It can't erase physical evidence, however, and Crazy-Prepared Urahara immediately notices discrepancies in his notes and memory and figures something's up.
Kaito of Mermaid Melody Pichi Pichi Pitch presumably gets a bump on the head that causes him to selectively forget everything about Lucia and mermaids. Of course, this turns out to be an evil plot (and a rather lucky one for Michel at that— he gets the energy from Kaito's memories and blackmail to try and convert Lucia to his side).
Happens to a lot of Kanon characters, all for reasons relating to the town's miracles and the tragedy seven years ago.
In Ranma ½, Shampoo uses a technique on Akane to erase all memories of Ranma. She remembers every other person and thing, even when not knowing Ranma means she wouldn't know how she became familiar with them. Apparently, Ranma's father is living with her for no discernible reason.
Shampoo's amnesia technique has the added benefit of preventing the victim from ever relearning the suppressed memory, so every time Ranma was re-introduced to Akane she'd forget the latest introduction as soon as he left her line of sight.
After accidentally smacking his head with a watermelon in a training accident, Kuno retains the formidable skills he gained through his watermelon training, but forgets his name, his pompous demeanor, and how much money he owes to Nabiki (none, but she's not going to say that). Worst of all, his self-restraint is gone, turning his infatuation with the Pigtailed Girl into a stalker obsession that nearly ends badly for her.
One anime episode goes beyond this into Loss of Identity; after falling into the pond and hitting his head, Ranma starts thinking of himself as really being a girl. "She" hates violence, wants to give up martial arts, faints at the sight of blood, freaks out and starts crying after being returned to male form, talks about becoming a bride and goes bra shopping with Akane, has to have Akane help her go to the toilet because "she" can't deal with either set of body parts, rebukes Akane for her tomboy ways and, after Akane finally breaks down and admits that this isn't Ranma and she wants the real Ranma back, "she" tells her that it can't happen. Fortunately, as with Laser-Guided Amnesia, Ranma is restored to normal after Akane knocks "her" back into the pool and makes him hit his head again.
Happens later on to Yue after the Gateport incident randomly scatters Ala Alba across the Magic World. She has the bad luck to land right in front of a magic student on a broomstick, who not only gives her a knock on the head, but accidentally discharges a memory erasure spell, causing her to lose all of her memories except her name.
At the start of the series, Negi attempts this on Asuna when she finds out he's a mage. It does not go as planned. Otherwise, Negima avoids this by having the masquerade instead of removing memories of crazy happenings, just prevent them from noticing all the craziness going on.
Lelouch Lamperouge from Code Geass uses his Geass to erase his close friend Shirley's memories of him because she found out that he was Zero and the man responsible for her father’s death and she now reluctantly wanted to kill him.
Around the same time, the character Viletta gets shot and falls into the bay, hitting her head and getting amnesia almost immediately after learning Zero's identity. Convenient.
Suzaku Kururugi had repressed memories from the start of the series after, at the age of 10, he killed his dad the ex-Prime Minister of Japan and doomed his homeland to Britannian rule. He was so traumatized that he blocked his own memories of the issue for years, until C.C. forces it out of him in a confrontation between him and Zero (though in her defense, she didn't have any idea of what she was making him see, only using her powers with the intention to stop him). Mao would do this later again via his Geass and some quick wit, cause a Mind Rape for the poor guy).
Later on, C.C. loses her powers and is temporally stricken with amnesia; for her, it's even more severe than the usual case, since she reverts to the state she was in at the last point in her life before receiving a Geass: a ten-year-old slave-girl from the Dark Ages. Though she can still speak...whatever modern language they're speaking.
Plus, at the start of season two, The emperor uses a memory-manipulation ability to erase all of Lelouch and his classmates' memories regarding Zero, Lelouch's heritage, and Nunnally. Is there anyone in this show who doesn't have amnesia?
Lelouch also does this to himself when Mao holds Nunnally hostage; in order to stop him reading his mind and finding out his plan to save her, he tells Suzaku what to do, then mindwipes himself before heading up to face Mao. It works.
In Hana Yori Dango, Tsukasa is afflicted with bizarrely specific amnesia that causes him to retain all of his memories except those specifically related to the series's heroine, his girlfriend Tsukushi.
In Interstella 5555, the main characters, an alien music group, are put in a machine that changes their memories to make them believe they are human.
Done very literally in Vampire KnightKaname uses his vampire powers to wipe out Yuki's memories of Maria being in fact Hio, the vampire responsible for the slaughtering of Zero's family. It does not last long, though, as the effects are almost immediately canceled by Hio herself.
In Death Note, owners of the titular object have the choice to give it up at any time, losing all memories of it in the process. However, any repercussions suffered as a result of actually using it (half-lifespan lost for those with the Shinigami Eyes, for instance) remain firmly in place.
This is a hilarious example of this trope being played absolutely straight. So Light and Misa, for instance, forget not only the existence of the notebooks and their use of them, but also everything incriminating relating to Kira, while retaining the knowledge that the mass-murderer Kira exists. It not only wipes their knowledge of their own guilt, but that of the other, too, right down to the presence of the secret compartment in Light's watch! It barely only makes sense if you assume that they're reconstructing the holes in their memory in order to make sense of them — "I had no means to kill all those people, therefore I can't be Kira, so obviously none of this can have happened".
In fact, we see this happen at least once, when Misa doesn't recall that she was detained on suspicion of being the second Kira until she's explicitly reminded of it. Mind you, Misa is The Ditz.
She's also a clinical psychopath, like Light and possibly L (who may just be in the autistic spectrum, or schizoid), and not nearly as much of an idiot as she makes herself be, though she looks pretty dumb compared to the resident geniuses even at the start, when she's making an effort.
As a clinical psychopath, Light wouldn't necessarily have done anything especially evil if he hadn't gotten the Death Note; he had a self-image as righteous to uphold and lots more to gain by remaining the golden boy, boring as it was, and the laser-guided-amnesia Nice Light is zapped right back to that—more than factual memories are removed; his considerable character development related to the Note gets reset. He keeps what L-related developments weren't actually part of Kira-hood, and the fact that his life is no longer boring because of the Kira investigation, but forgets about his break with normative humanity. Lots of clinical psychopaths interact perfectly normally in society, and the smarter ones tend to wind up in its upper echelons. He would have, too, if he didn't crash and burn from frustration with it all being too easy and meaningless.
Though still commonly heard in casual contexts, it's been thirty years since the term "psychopath" was clinically accepted, and the usefulness/precision of its successor term, "antisocial personality disorder," remains in dispute.
The persons affected can't be consciously filling in the holes based on logic, because then Nice Light would know from looking at the holes in his head that L's theory about amnesia is completely correct, and he doesn't buy it. The magic at work is obviously complicated stuff.
In Nanaka 6/17, the titular Nanaka, after being told off by the Childhood Friend she kept nagging and then taking a header down some stairs, loses all memory of everything that happened to her after the age of six. Nanaka's six year old personality simply assumes a wish she'd made to grow up right away actually worked.
Gundam Wing: (Trowa Barton survives a terrible fight against his best friend Quatre (who was under the effects of the Zero System), but loses his memories. Don't worry, Quatre helps him get them back. Best friend? Some would say Ho Yay!
Watanuki from Xxx HO Li C is a very interesting case. His magically induced amnesia is not only partially anterograde (for example, he can't remember the taste of anything he eats, or even remember if he ate it), but it's also done in such a way that he didn't even notice he had it for quite some time. The discovery gave him a tomato related nervous breakdown.
Later in the same series, everyone except close friends and relations forget who Yuuko is when she dies. She'd been living on borrowed time and so the universe rewrites itself to be as if she'd died when she was intended to. Actually, part of the reason why Watanuki's desire to see her again seems to manifest such a severe obsession that he'd adopt her mannerisms and wear her clothes, is because of his fear that one day he'll start to forget her too. If he keeps her belongings close to him, he figures that they'll serve as reminders to prevent that from happening.
One of the types of mushi in Mushishi can cause this, erasing all of your personal memories up to that point. This is precisely what happened to Ginko as a child, something that also left him unaware of his other condition...
Used regularly in Fruits Basket, whenever someone learns too much about the Sohma family, thanks to the local doctor and family member Hatori Sohma. Tohru is threatened with this, Momiji's mother chose to forget him because she could not cope with the curse, and Kana had to go through it after being put through Mind Rape.
Implied in Axis Powers Hetalia with Ludwig aka Germany. If this is the case, he probably lost his childhood memories of being the Holy Roman Empire as time passed and he fought in too many wars.
A reoccurring plot point in Fushigi Yuugi, first seen when Yui feeds Tamahome a drug to make him forget who he is and turn evil.
Second, as Amiboshi turns out to be Not Quite Dead but doesn't remember his past at all. The amnesia was guided by his new family, who are big fans of this trope and try to "help" Miaka by pointing some amnesia her way, too.
Although Amiboshi was largely faking it; he preferred his new family.
Done again to Amiboshi by Suboshi, no less. Amiboshi tells his twin to not fight the Suzaku warriors and take the amnesia-inducing juice/soup. Suboshi does and kisses Amiboshi because Suboshi doesn't want to forget Yui, on whom he has a crush.
Third, in the OVA series, Tenkou uses MacGuffin Spheres to systematically erase Taka/Tamahome's memories of his allies.
Crops up several times in Mx0, like Taiga's memory of the entrance exam and the Lotus-Eater Machine portion of the exam, in which leaving the 'machine' let you pass but erased your memories (which you kept if you failed).
Double Subversion in Tekkaman Blade: D-Boy turns out to have been lying about having amnesia, and remembers everything. Then later, he starts losing his memory for real.
In Excel Saga Excel gets amnesia after Il Palazzo shoots her and leaves her for dead. In this case, it's unclear if she repressed her memories or lost her memories because she was hit by a car.
In the manga Excel gets this twice. The first time was brief and played for laughs. The second time it lasts a lot longer, and her personality is flipped. It is also suggested this isn't the first times she has lost her memories.
Elie gets this twice in Rave Master. She doesn't know her name or how to control her magic, but she can remember how to read a language no longer used in the modern world.
In History's Strongest Disciple Kenichi, Elder Furinji has a technique called, 'Shockwave of Forgetfulness', a soft punch that can cause the victim to lose his memory. He did it once on a crimelord in Thailand to make him forget he was evil, and again on Kenichi- to make him forget about the really expensive drawing Elder bought, which he was going to tell Miu about.
Fairy Tail: Jellal, who doesn't remember any of his past crimes or his own terrible life. The only thing he remembers is the name Erza.
Pai suffers from a supernatural case in 3×3 Eyes. Pai and her grandparents believe that she's an Ordinary High School Student who lost all of her memories in a bus accident, but in actuality she's a 300-year-old immortal Sanjiyan Unkara who had her memories sealed by The Dragon so she couldn't interfere with their plans. They even gave her and an old couple false memories and photos to give her a "backstory" and a belief that monsters don't really exist.
This sealing also has a tragic twist: The Dragon used a minor demon called Houasyou as a basis to "forge" the seal on Pai, who would enforce the seal and keep the Sanjiyan Unkara dormant. But since Pai has a split personality between a Genki Girl and Tsundere, the seal has an unexpected side effect — Houasyou herself lost her memory, and thanks to the Masquerade, she believes that she's Pai. And when the good guys finally confront The Dragon to get her memories back, that means Houasyou has to accept that she's actually a demon and won't be able to be with her love Yakumo because he loves the real Pai, not her.
Yu-Gi-Oh! GX: After suffering from nightmares for an unknown period of time because of Yubel being in pain after being shot into space, Juudai was given the most advanced treatments to completely block out his memory of her. This also apparently blocked out his memory of the contest he'd won and the Neo-Spacians that he'd created. He didn't remember Yubel at all, however, until he actually saw her in her own true body again.
Yu Gi Oh: In the first series, one of the most important plot points was to recover the memories of the Nameless Pharaoh, aka Yami Yugi. It turns out he himself gave up his memories and bound his soul to the puzzle in order to seal a bigger evil, which had to be defeated near the end of the series.
Milk Crown and its sequels. The protagonist, Oto Tachibana, loses her memory at least three times, if I remember right... It's been awhile since I've read the series...
Karin: The vampires can hypnotically erase memories of the feeding from the people they bite.
In the manga, this happens to Karin herself. Once she's freed of the curse, she no longer has any vampire traits, so her family erases her memory of them in order to allow her to live as a human, who thinks she was orphaned. Apparently, they'd been planning to do so for four years, preparing her mind so that she would only forget about vampires and nothing else.
In the second, 80s series of Himitsu no Akko-chan, the titular heroine carelessly outs herself as a Magical Girl in front of her whole community of friends. While at first her empowering entity doesn't take it well, stripping Akko of her powers and her reflected image, later settles for a new, stealthier mirror and free Laser-Guided Amnesia for everyone involved.
Necrolyzation has this effect on people in Gungrave. It also usually strips the reanimated person of emotions as well. The protagonist undergoes said process and suffers terrible headaches whenever he recovers a fragment of his memory. Conversely, in the videogame he doesn't get the headaches, and never quite gets over his memory loss—with a fewcrucialexceptions.
Masako Natsume from Mawaru-Penguindrum plays this trope to a T by using her laser-guided slingshot to have all Kanba's ex-girlfriends to forget about him at all.
In Switch, Kai lost all his memories from before he turned six.
In Gunnm, Doc Ido suffered total mental collapse when Desty Novas revealed the dark secret of Tiphares: all of the citizens of Tiphares, such as Novas and Ido, get their brains replaced with chips at the age of nineteen. Unable to live with this revelation, Doc Ido recorded a final farewell to Alita, erased his own memories a feat made relatively easier since he has a chip for a "brain", and started life anew as an ordinary doctor.
Washu does this to the OVA Tenchi Muyo! cast in one issue of the manga. Dr. Clay starts attacking the crew via an old assistant robot of Washu's and forces her into a Sadistic Choice - either fight the robot alone and forget the others, or watch as the robot continues attacking everyone she cares for. She chooses the former and erases everyone's memory of her... but only them, which allows Minagi, a clone of Ryoko, to spot Washu taking Ryo-Ohki to the fight site and be able to push the gang into realizing something's wrong. When they confront Washu, she ends up undoing the Amnesia (which pisses Tenchi off that she did so in the first place), but Sasami ends up undoing it on herself while they're gone.
Happens to Yumina in one of the bonus episodes of So Ra No Wo To, when she and the main cast (except Kureha) get extremely drunk. Their secret distillery is semi-illegal, and Yumina is a priestess, so she conveniently forgets about the whole thing. Somewhat justified since alcohol can have this effect, but it's awfully weird that she doesn't notice having no memories of the previous night, and she doesn't even get a hangover to go with the blackout.
Astral in Yu Gi Oh Zexal suffers from this. At the beginning of the series he cannot remember anything about his history or purpose, and can only regain his memories by collecting Number Cards with Yuma.
Captain Dan in Planet Robo Danguard AceIchimonji Dantetsu, the hero's long-lost father turns up with an un-removable mask after 10 years as the villain's mind-controlled slave - the mask has not only removed his memories from before it was put on, but seems (since a convenient memory-viewer establishes that he has no memories prior to the accident that broke the mask's control mechanism...) to have prevented new ones forming - however Dan retains his almost unstoppable willpower, a drive for excellence (and revenge!) AND his ace piloting skills which are practically off the charts... After one too many bumps on the head he gets better.
Ramia is struck with this in the third Pretty Sammy OVA, "Super Kiss". She encounters an alien lifeform which absorbs all over evil traits, leaving her to wander the beachside as a kindly young woman as Rumiya and Pixy Misa try to find her - both Tsunami and Sasami have no idea what's going on as Tsunami thinks that Ramia is there... which is a doll in front of her. She quickly remembers everything, though, when she finds Pixy Misa and Pretty Sammy fighting the creature.
In an early Incredible Hulk comic, Betty Ross is kidnapped by baddies and taken to their underground lair. Hulk goes down and rescues her (at the time, the Hulk was intelligent), beats the baddies and proves that he's not evil after all. During the tram back up the mine shaft it's revealed that Betty has forgotten the whole event due to stress. This is while she's still in the same room as the guy who just rescued her.
Virtually all of Wolverine's character and most of his plot arcs are based around his adventuring past which he cannot remember — or remembers wrongly. Around the time his origin was finally revealed, it came to light that his Healing Factor works in a psychological capacity as well, and actually scabs over especially hurtful memories.
In the 1950s, this was used as the basis for a Heel Face Turn by Catwoman, in the same story that introduced her now-canonical civilian persona of Selina Kyle.
The third Flash, after years of having his identity public, enlists the aid of the Spectre to erase everyone's memory of his secret identity. People remember both The Flash, and Wally West, but not that they are the same person. In an unexpected side effect, this initially affects Wally himself.
In the DC miniseries Identity Crisis, it is revealed that one of the reasons the JLA has been able to keep their identities secret over the years is by having Zatanna strategically erase the knowledge from the minds of any villains who find out. The story was set into motion years before when they attempted to forcibly reform Dr. Light via this method, and it went horribly wrong.
Their mindwiping wasn't just limited to villains; Batman was also mindwiped.
Only of the fact that they were mindwiping villains, though—but since he can't be sure of that, the emotional factor is...ouch.
The meta-reasoning for this was to give Batman a real reason for every Batman Gambit plan he ever had in mind for his friends.
Following one of the times his identity was made public, Iron Man used a villain's mind control powers to wiped the memory of everyone on Earth. This is supposedly before the Dork Age of Smug SnakeCivil War Tony, although it may have been one of the seeds of this (notably, Captain America was very unhappy).
Before Planetary recruited him to become the third man, Elijah Snow lived in a shack in the desert with gaps in his century-spanning memory you could "chuck a nuke through". His work with the field team leads him to prod at these gaps and learn that the mysterious Fourth Man behind Planetary is him, and that The Four forced him to allow the memory blocks after they captured him and his team.
In Don Rosa's Uncle Scrooge story "Forget It!", Magica uses a wand that causes anyone hit by it to start forgetting things related to words they hear after they hear their name, and uses it on Scrooge and Donald Duck in her latest effort to steal Scrooge's Number One Dime. Hilarity Ensues as Donald and Scrooge forget how to use doors, stairs, and even how to stand up and walk due to Magica's spell.
In Carl Barks' "House of Haunts", Scrooge was also given amnesia by the Beagle Boys by a blow to a specific spot on his head. This gave Scrooge the specific amnesia of forgetting everything that happened since last November. Tapping again apparently is a complete cure.
In Supergirl: Cosmic adventures in the 8th grade Belinda flicks a "memory erasure pressure point" on Lena Thorul's head, which makes her forget all about Supergirl's secret identity. Supergirl refuses to believe it worked. The actual amnesia was caused by Streaky the Super-Cat's psychic powers.
Mandrake The Magician has had parts of his memory erased several times, usually by well-meaning, but condescending aliens and time-travellers who thinks it's too dangerous to let him remember all the fantastic things he has seen. The poor guy's had a lot of amazing adventures that he will never know about.
Not so long ago it happened in Thunderbolts: When they have to kill Songbird, Headsman, Ghost and Paladin betrayed and defeated Scourge and Mr. X, and left her escape. Then Ghost removes this even from Scourge's and X's short-time memory
When Maxwell Lord was resurrected in Blackest Night, the first thing he did was to use his Psychic Powers to mindwipe everyone on Earth of all of their memories related to him except for his old Justice League International teammates and the Blue Beetle scarab. He went even further to maintain the illusion by implanting Fake Memories such as Ted Kord committing suicide and Ice trying to murder Guy.
Which causes still-unexplained plotholes, as several people implied affected expressly would not be given the storyline. While it's unlikely that, for instance, Kilowog would bring Max up in casual conversation, or that an egomaniac like Manga Khan would give Lord a second thought, Wonder Woman was expressly described as immune to his powers, which is why she was able to kill him in the first place. She's affected like all the rest.
One issue of Damage Control had the company hired to repair damage to Xavier's School For Gifted Children from a super-battle. After the repairs were completed and the crew paid, Professor Xavier used his telepathic powers to erase their memories of the school's location and students.
In Fleetway's Sonic The Comic, when Super Sonic was split off from Sonic, he completely lost all memory of what he was. He forgot that he was an embodiment of pure malevolent evil. He even lost his super-super-speed and world-destroying powers because he forgot he had them and became just a regular kid for a while. Of course, Super Sonic being normal is exactly as interesting as it sounds, especially since he was portrayed as a borderline loser, and it didn't last.
In the New 52 version of Stormwatch, the Martian Manhunter wipes the memories of superheroes he's forced to interact with, so they don't know about Stormwatch. When he leaves the team, he wipes all their memories of him. He implies he's done this sort of thing before, which may be considered a Fridge BrillianceRetcon as to why Stormwatch think he's also been a conventional superhero, but the heroes he contacted have never heard of him; he's already wiped their memories of his public career!
This was used to explain how Spider Man was able to rehide his secret identity after Civil War. In One Moment In Time, he convinces Iron Man, Mr. Fantastic and Doctor Strange to help him fix this. A combination of Strange's magic, Reed's nanobots and Tony's Extremis link allow them to erase everyone's memories of Spidey's identity... except for Mary Jane's, which Peter makes sure doesn't happen. Peter later broke the spell, unwittingly, during Spider Island, when he revealed he was one of the many who had spider powers. The knowledge of who he is remains wiped from everyone's memory, but now others can find out.
In Red Hood And The Outlaws #19 , Red Hood has S'aru remove every single memory of his that The Joker touched to let him start anew. Unfortunately, this is almost everything he remembers. By the end, he doesn't have the slightest clue who Arsenal or Starfire are.
In Pokemon Mystery Dungeon Silver Resistance Char, the protagonist, has this to the extent that he doesn't even remember his own name(Char being a nickname given by Saura). Subverted with Saura, who we thought was invoking this trope after being Mind Raped.
In Speechless, a Death Note fic, this shows up.
A Star Wars fanfic called Innocence sees Vader suffering brain damage after a crash into Rebel territory. When he learns the facts of his career, he decides he'd rather start as a new man. While he's unsuccessful in getting rid of his breathmask, he adopts some less intimidating prosthetics and swaps his black cape for green coveralls. He rediscovers his engineering talent with Han as a mentor/bodyguard, and after helping the pilots get even with an obnoxious commander, is ultimately accepted as a comrade.
Mistakes depicts the nation-tans of Axis Powers Hetalia as unable to disobey a direct order from their human leaders. Thus, when Japan finds out the horrible things being done to his brothers and his boss tells him to forget about it, not even meaning it entirely literally, Japan does.
In the Clannad fanfic An End To All Things, this is the result of some sort of accident, and is the reason why Okazaki doesn't quite remember Kotomi.
General: It's probably easier to list fandoms that haven't had at least one fic with this trope in it. Usually, the protagonist loses several years and forgets their identity, job, and significant other, and falls in love with said lover all over again.
Films — Animation
Literal example in Pixar's Jack-Jack Attack, and explicitly shown in a cut scene from The Incredibles. Plays a little like mind rape, since Huph is trying to hold on to the original version of the events.
Used in Wreck It Ralph by King Candy to make everyone forget that Vanellope Von Schweetz is the actual ruler of Sugar Rush instead of a glitch.
The film The Vow is based on a real life story of this.
Films — Live-Action
The Paycheck film features literally Laser Guided Amnesia (neurons destroyed with lasers), as a method to prevent engineers to trade out top secret technology after finishing their assignment.
It also appears to work flawlessly, but can only be used for erasing short periods of time (up to a few weeks). For longer periods, they switch to a chemical agent which is supposed to do the same job. It doesn't work quite as well, leaving behind pieces of memories.
One skillfully executed example is the 2004 film Eternal Sunshine of the Spotless Mind, which concerns a company that can specifically erase your memory of a particular person, used (for example) when a subject wishes to forget a devastating love affair. The explanation of the process is mainly technobabble, but is believable and internally consistent, with some noticeable secondary memory loss.
X-Men Origins: Wolverine features quite possibly one of the most painful instances of this trope. An antagonist loads a gun with Adamantium bullets, knowing he can't kill Wolverine with them, but intends to give him Laser Guided Amnesia by shooting him in the head. He succeeds, wiping Wolverine's memory with no other side-effects.
The Neuralizer from Men In Black, also known as the "flashy thing". It can be set for a specific length of time and leaves the victim in a brief trance so a cover story can be planted to maintain Plausible Deniability. Agents are also issued special sunglasses to prevent accidental self-neuralization.
The entire Bourne (Identity, Supremacy, Ultimatum) series of films have a protagonist who has amnesia induced by a psychotic break while on a mission. His amnesia could be organic as well as psychological, since it's implied that he and his fellow assassins are/were taking some sort of medication to supplement their conditioning, and he's obviously not taking it anymore. It could be why he can't recover any of his memories, despite his best efforts.
Happens to Alice and Spence Parks in the first Resident Evil movie as a side effect of being rendered unconscious by sleep gas.
In the 2009 film Push, there exist people called Wipers, who can temporarily or permanently erase memories, useful as there are other people in that universe who can read minds and memories. Wipers can wipe all memory up to a certain point, or try to wipe only certain memories relating to specific topic, but the accuracy of the wipe is determined by their skill.
A strange mix of anterograde and retrograde amnesia is played for laughs in Clean Slate, where Dana Carvey's character has forgotten his entire past and forgets the events of each day as soon as he goes to sleep.
In Cypher, Applied Phlebotinum is used as a brainwashing tool in order to turn employees of a Mega Corp into unknowing corporate spies. Whilst they don't completely forget about their formers lives, the corp makes their new "fake" lives such a facsimile of the old one that they never notice.
The central premise of Dark City. A man wakes up with no memories of his identity, but has lingering emotional resonance with certain people and places. How much of his personality is truly his remains a mystery — it's implied that his love for his wife is genuine, but at the same time, he's also driven to visit Shell Beach, a place everyone's visited but nobody can describe its location. It doesn't exist, until the end when he makes it exist. He finds his mindwiped wife there, and the movie ends before revealing whether her feelings toward him were genuine or induced.
Invoked in the Korean Lost and Found. After a car accident reunites her with her high school crush, the protagonist pretends to have amnesia so that he'll have to take of her. Her doctor lampshades it, saying she seems to have gotten "TV amnesia" that wiped her memory but left all her other skills intact.
The Recognition of Shakuntala, an episode from the AncientSanskrit epic Mahabharata that was later Expanded into a theatrical drama by the Indian playwright Kalidasa around the 1st century BC, is probably the Ur Example of this trope. It's a Girl Meets Boy story revolving around a woman named Shakuntala who meets a guy named Dushyanta and they get married him, only for him to get cursed with Amnesia and completely forget her. The only way to lift the curse is to show him the ring that he gave her, but she loses the ring in a river. She eventually finds the ring by the end of the story, makes him remember, and then they live Happily Ever After.
In Dan Abnett's Gaunt's Ghosts novel Traitor General, Sturm's "mind-lock" prevents him from remembering his life before his capture, though he has formed memories since.
Premise of the 1973 spy thriller The Tightrope Men. The protagonist wakes up in a hotel room in Oslo, not only unable to remember who he is, but with an entirely different face and identity. It turns out that he was kidnapped, brainwashed, and cosmetically altered to cover the abduction of the scientist he resembles. The only thing keeping him sane is that he still can remember some things, like his name, from his previous life — the brainwashing was a hastily-done "butcher's job". The author Desmond Bagley said he thought up the most terrifying circumstance you could find yourself in and then wrote the novel around it.
Bagley had previously used the amnesia motif in Landslide (1967), whose protagonist has forgotten all personal information, includinghis own name, in a car accident. That he hasn't forgotten the geology he studied before the accident becomes a minor plot point.
Subverted in The Wrong Reflection by Gillian Bradshaw. The Hero wakes up not knowing his own face or history and not fully able to operate in society. He needs help in figuring out that he has basic human rights and in one example, doesn't know what an 'oak tree' is. He knows science inside and out but the concept of 'muzzling' is a mystery.
The vampires in the Black Dagger Brotherhood can fuzz out specific memories in human's brains, and can also mess up security cameras for specific amounts of time, all in order to stay anonymous in the general human populace.
In Memory, Chief of Imperial Security Simon Illyan's implanted eidetic memory chip breaks down and has to be removed before it will kill him. Though he doesn't suffer any retrograde amnesia, for him to suddenly go from perfect memory to normal memory is treated as something almost as bad, and he does suffer from a period of anterograde amnesia for several weeks as his brain has to "relearn" how to memorize things for itself.
In Shards of Honour Bothari is given a brutal drug-aided memory-suppression to remove politically inconvenient memories (mutinying and murdering his commanding officer, who thoroughly deserved it). He manages to hold on to a few memories, however.
Elena Visconti, a POW who had been raped and tortured by both Bothari and his CO, had her memories removed because the surgeons felt sorry for her. Of course, when she got home the psych officers promptly removed the blocks. Twenty years later, she's still a bitter, angry wreck. Nice Job Breaking It, Hero.
In Artemis Fowl, the fairies have mind-wiping technology which can be fine-tuned to suppress only specific memories.
The process is not perfect, however. Exposure to stimuli regarding the repressed memories can bring them back. Of course, the fairies monitor most subjects of this to ensure that this never happens. And since they run a huge Masquerade, the odds of a fairie-induced amnesiac regaining their relevant memories are extremely low.
In Umberto Eco's The Mysterious Flame of Queen Loana, the protagonist suffers from amnesia that leaves him with only his semantic memory, erasing whatever he had made a personal connection with. He's left with memories of the books he's read and of various subconscious procedures (e.g., writing his name on a check), but not of his wife or his childhood.
In Alan Dean Foster's Humanx Commonwealth universe, a technique called "selective mindwipe" can be employed to surgically remove memories from a person's brain. The Commonwealth itself only uses mindwipe in cases of particularly heinous crimes, as an alternative to execution, but there are insinuations that it's used by less savory groups to prevent people from ratting them out. The most often cited use of mindwipe is on the members of the Meliorare Society.
Sergej Luk'yanenko's Genome features a progressive mindwipe (from birth to present, keeping the victim aware of the process) as capital punishment in a regicide case. The body is then sold to a willing bidder, although the protagonist rightfully assumes being the Unwitting Pawn. A fugitive transhuman female leaves with the mindwiped transhuman male body and the stolen (or liberated) digital male personality of her creator/lover. Now assume that said lover knows how to download himself.
The last three books of the Sword of Truth series hinge on a spell that makes the whole world forget that one of the main characters ever existed, including fabricating memories to compensate for events she was present for or even responsible for and it makes people forget she exists right when they are looking at her. To the point of being able to literally walk naked down a crowded camp and almost no-one looking twice. Because of a contamination in the spell, though, it starts to unravel the world of magic as a whole.
In Simon Hawke's Time Wars series, the 27th Century time travellers have a Laser-Guided Amnesia technique they use on contemporary people who have been involved with them. However, in The Nautilus Sanction, which involves the Big Bad stealing a Russian nuclear sub, equipping it with a time machine and bringing Jules Verne on board, they decide that giving Verne amnesia might interfere with the creative mind, and so they arrange to keep an eye on his subsequent work.
In Rudyard Kipling's Puck of Pook's Hill, Puck gives the children amnesia to prevent their talking about what he told them.
In Daniel Keys Moran's The Last Dancer an extremely long-lived (possibly effectively immortal) human from the distant past, future or a different time-stream (in-universe they are not substantially different concepts) arrives on earth several tens of thousands of years ago local time. Because of their long lifetimes, one of the abilities his society has developed is a method of "archiving" your own memories - like ZIP for the brain - so that your brain doesn't fill up over the eons, while still being able to retain older memories. Exceptionally long periods of meditation are required to organize and archive your memories in this way, which can result in a sort of self-imposed amnesia since you can decide what memories will get archived. He then suffers from head trauma that gives him Laser-Guided Amnesia and he mostly forgets his history, retaining the knowledge that yeah, he lives for a very very long time and a few scattered recent memories that he tries to piece back together over time. Averted in a sense because all his archived memories are still present, only it takes his brain a couple hundred years to heal over and recover the memories until he reaches a point where it all snaps back into place.
Harry Potter features the Obliviate Charm, which wipes a person's memories based on the skill of the caster. The charm can have some nasty side effects, though; when Gilderoy Lockhart tries to use the charm on Harry and Ron while clutching Ron's broken wand, it backfires and wipes pretty much his entire memory. Interestingly, Lockhart's amnesia follows the rules to a T, except for the fact that he apparently forgets Functional Magic is real. This raises the possibility that the malfunction might've caused the Obliviate effect to do to Lockhart exactly what it's designed to do to Muggles: wipe out all recollection of the wizarding world or its magics. Since Lockhart isn't Muggle-born, this would erase his entire past, which is precisely what happened.
The Obliviate Charm is played for laughs in Harry Potter and the Goblet of Fire when the very perceptive and suspicious Muggle groundskeeper that is unknowingly renting out space for the International Quidditch Cup fans has to be repeatedly charmed to keep him unknowing. Played for drama again when it's revealed that Crouch Sr. erased Bertha Jorkins' memory of Barty Crouch Jr. with a Memory Charm powerful enough to damage her memory permanently, leaving her an absentminded and bumbling shadow of her former self.
The more recent Star WarsExpanded Universe novels have Jacen Solo discovering a method of short-term memory erasure, which he uses to hide from his apprentice, and others, memories that would point to his being a Sith Lord. It's called "rubbing".
Wright's The Golden Age opens with Phaethon first learning that he did something so disgraceful that he ought to be ashamed to show his face, and being urged by a Neptunian to flee at once to them, so they can repair his damaged memory and personality. Things progress from there until the plot verges on a Gambit Pileup.
Forget charms in The Hollows novels remove specific memories from anyone they are used on. Rachel has had them used on her twice. The first to remove all memories of the illegal genetic treatment she received as a child. The second was given to her by her own partner to remove the memory of her boyfriend's murder so she would not go after the vampire who killed him and get killed herself. In the second case though she got better.
The second use of the charm was notable in that the information removed from Rachel's mind is also removed from the book itself. The narrative skipped over the parts removed from her memory. Readers had to wait until Rachel's memories returned two books later to see the scene for themselves.
In Warhammer 40000, this is inflicted on Grey Knight aspirants, of all their lives before they became Grey Knights, as a means of protecting them against Chaos. In Ben Counter's Grey Knights, Alaric explains that he had been taught that it would be done to him, but he doesn't remember being taught it. Then, none of them have ever succumbed to Chaos, so it did have its benefits.
Sharon Farber's chilling short story When the Old Man Waves the Banner is built on anterograde amnesia, induced with brain surgery; this being the only way the rebels can send an assassin to kill a dictator who can telepathically detect and deflect assassins. The protagonist has all his memories up to the operation, but can no longer recall recent events beyond the past 10 seconds or so. Against expectations, he survives after the assassination, with unfortunate consequences.
Terry Pratchett often uses the concept that humans forget events that are too vast to be comprehended in order to remain sane. This often leaves lead characters remembering saving the world only to have everyone else think they've gone off the rocker. Since they're usually wizards, nobody really cares.
In The Dresden Files any use of mind magic, including memory modification, is against the Seven Laws of Magic. Violating this law can be punishable by death so the necessary magics are regulated by the White Council. However, this restriction only applies to human users of magic. At one point, SusanRodriguez gives a year of her memory to Harry's FaerieGodmother, Leanansidhe, in exchange for Harry to stop suffering the effects of a broken bargain. Lea takes all the memories that Susan had of being in a personal relationship with Harry. She got better. Then it got worse.
In Deerskin, the female protagonist is raped and impregnated by her father, and institutes this on herself to such an extent that she can literally remember almost nothing but her own name. Later, when the memories return by force, a Deus ex Machina takes them away again until she can grow strong enough to deal with them.
In Neil Gaiman's Stardust, one witch inflicts this on another. And it screws her over later because the curse makes Sal unable to even be aware of Yvaine in any way, so when she later questions Sal to see if Yvaine's on the cart, Sal 'truthfully' says no.
George Martin's Wild Cards series features inducing amnesia as an Ace power:
The Astronomer, on top of his already impressive list of mind-related abilities, can or suggest to do so:
He has removed all memories of his own pre-Wild Card life from himself, as he probably perceived those as a weakness.
He offers Roulette to wipe the memories of giving birth to a hideous still-born joker baby, although channeling this traumatic memory actually powers her Ace - killing men during intercourse. She is fine with losing her Ace and forgetting the "career" as Ace assassin.
Demise was going to die by drawing the Black Queen, but was saved by the experimental Trump cure, although this resulted in a rather unusual Wild Card. Demise's Ace now includes very limited projecting telepathy - he can project the memories of death to stun, shock or kill. Similarly to Roulette, the Astronomer offers Demise to wipe those memories as a severance pay of sorts - this would make Demise a much happier and much less dangerous Ace.
In L. Jagi Lamplighter's Prospero Lost, Tybalt, Miranda's familiar, says that the Eleusian Mysteries were an attempt to gain the secrets of the cats, and explains that everyone must drink from Lethe to return to life, except cats, who can live without that eight more times. (If a cat hasn't learned to stay out of trouble after nine tries, they figure he might as well start over.) The Mysteries tried to make the initiates Demeter's adopted children, and so the Maiden's adopted siblings, so she would let them off out of nepotism.
In Donald E. Westlake's final novel, Memory, the protagonist, Paul Cole, suffers brain damage after sleeping with another man's wife. At first, he's fine, but as the story goes on, he loses most of his memory function. He can remember things, but they leak out of his head. It does not end well.
In Matched, everyone is required to take around three pills. The red pill wipes your memory of the last 2 days. This is used to keep people from remembering things that are out of the ordinary.
In False Memory, Dr. Ahriman does this to damn near everybody around him. He has all his patients and most of his staff conditioned to respond to code words, which allow him to put them into a hypnotic trance and make them do whatever he wants. Sometimes it's practical, but it's often really, really squicky.
"You don't remember anyone or anything, except when you do, of course. You can't operate the TARDIS any more, except when you can. You don't know what happens in the future, except when you do. Drop the act, it got old years ago."
Early in the Jane Lindskold book Thirteen Orphans, several characters are subjected to the spell that strips them specifically of memories pertaining to their shared heritage of descendants of an emperor and his advisers who were exiled from their homeland. All other memories remain intact, though when one of the antagonists, raised in this knowledge all his life, his hit by the spell he loses all memory.
In the 13th century Völsunga saga, the evil queen Grimhild serves an oblivion potion to the hero Sigurd that makes him forget his fiancé Brynhild, but nothing else.
In Confessions of a D-list Supervillian Mechani-Cal used a device to help the world forget their addiction to the Defeated mind-control bugs. Later it is used on his new girlfriend and Superhero Aphrodite by her EX to forget her feelings for Mechani-Cal.
In Poul Anderson's "A World Called Maanerek", the hero had his mind blanked to see what would happen in another culture. Then it was blanked again and the original restored. Turns out it wasn't as neat as they thought — he remembers something both ways.
In the historical novel Wings of Dawn: Thomas. Granted, he hasn't been to the Holy Lands since he was very young.
Buffy the Vampire Slayer: "Tabula Rasa". After a memory spell goes wild, everyone gets amnesia and promptly forgets that they believe in vampires, including monster guru Giles. Moreover Spike, a 19th-century vampire, starts acting like a 21st-century human.
They not only forget that, they forget even their names and identifies
Subverted in the episode "The Pack". Xander, under the influence of a hyena spirit, alienates his friends, devours a pig alive, and tries, ineffectually, to rape Buffy. Afterward, he claims selective amnesia, convincing his friends that he won't have any lasting trauma. When they've gone, however, Giles points out that none of his possession lore mentioned anything about amnesia. Turns out Xander's been fibbing.
Power Rangers Turbo: Divatox gets amnesia and starts acting like an ordinary, if uncouth, human — and she isn't even human, nor has she ever lived like one. Her amnesia was the side-effect of a laser beam.
Power Rangers RPM has Dillon, whose memory was wiped as one of the Big Bad's unwilling test subjects prior to the series.
Power Rangers Wild Force: Cole gets amnesia in one episode. He forgets who he is and that he's a Ranger but nothing else.
Mighty Morphin' Power Rangers: In one episode, Lord Zedd turned a kaleidoscope into a monster with memory-erasing powers to make the Rangers forget who they are and how to use their powers. They were saved by Bulk and Skull, who tricked the monster into making the monster hit two prisms with his memory-erasing beam, (by passing a prism, it becomes a memory-restoring beam) and restoring the Rangers' memories. The monster made Bulk and Skull forget their recently-acquired knowledge of the Rangers' identities.
In the Super Sentai series Mahou Sentai Magiranger, a Monster of the Week puts a spell on The Chick, causing her to forget not only the plot she'd stumbled upon, but everything to happen since she became a Ranger. Every hour, all new memories are erased, too. Thanks to the broad amnesia, nobody suspects that the intent was to erase one specific memory. Still this trope, since the cutoff point for her memories seems pretty precise.
Stargate SG-1: Vala loses her memory when a memory-enhancing device malfunctions. Despite the fact that it's mentioned pretty directly at the beginning of the episode that she has very little experience with "normal" Earth-bound human life, her memory loss isn't so severe that she "forgets" how to pass for an earth-born human, or that she ought to have a hard time believing the actual circumstances of her life.
The same series also gave us "Fallen" in which Daniel, having descended from his higher plane of existence, has no idea who he is. This was quite intentional on the part of the Ascended. Even after Daniel regains memory of his mortal life, his time as an ascended being is very much forgotten, apart from a few glimpses.
There is also an episode where the entire team get their real memories erased and replaced by Fake Memories so that aliens can make them work in a mine.
And "Fire and Water" from the first season, though in this case the guy in charge overdid it, which the team spotted soon enough.
Stargate Atlantis also has a hand at this trope in the episode "Tabula Rasa" (not to be confused with the Buffy episode, though Joss Whedon probably named them both). After contracting an alien virus, the entire Atlantis expedition (save Teyla and Ronon) contracts amnesia, leaving a bunch of bewildered scientists trying to escape soldiers who have forgotten why they're rounding everyone up. The characters also suffered from anterograde amnesia, having some difficulty remembering what they were doing.
Torchwood: Retcon, a drug that not only induces specific partial amnesia but encourages the recipient's mind to "fill in the blanks", which usually prevents the victim from realizing they've been "retconned". A single image, say an alien murder weapon, can trip the amnesia if you're clever.
Also in Torchwood, Gwen ends up admitting her affair with Owen to Rhys and after clearing her conscience, gives him a drink with Retcon in it, so he doesn't remember.
In an aversion of #4, it's revealed late in the first series that Suzie Costello, before she died, had been going to a support group and gushing to one man about everything she needed to get off her chest from her job, then retconning him every week, for years. Given that retcon isn't generally applied more than once to anyone for fear of unknown overdose effects, and the guy is pretty nuts by the time they find him, this is horrifying.
Smallville erases the memories of anyone who finds out about Clark's real identity. Really. It doesn't matter how you found out, what you saw, or what he did under the influence of this week's phlebotinum. Your memory will be wiped, often without explanation. Amnesia is the Smallville Flu.
Lana, Jonathan and Pete forget everything after they are cured of the nicodemus flower's toxin.
Chloe forget all about Clark's secret after the parasite inside her is removed.
Judging by what happened to Lois's memory after her love potion wore off, the writers seem to think that all drugs erase your memory. Really, a love potion does that? You wake up next to someone with no clue as to what happened? Popping paracetamol must be a risky business in Smallville.
We've lost count of the number of times a bump on the head has wiped Lana's memory of seeing some super heroics.
An illegal immigrant gets to find out and doesn't get amnesia by the end of the episode, however.
This was used often in the first and second season to allow the advertisers to imply that the final conflict between Lex and Clark was at hand. It never was.
In more recent seasons, nearly every important cast member but Lex is in the know, so there's less need for this. The superhero cameos learn quickly, but keep the secret since they're on the same side.
In a rare example of plot-central, rather than "convenient", amnesia, Season 3 has Lex undergo a mind-wipe disguised as electroshock therapy for his supposed schizophrenia. The writers apparently didn't know that electroshock therapy is an extreme treatment for depression, not schizophrenia, and that it only removes minutes of memory, not months.
ECT (Electro-Convulsive Therapy) can indeed wipe months or even years of memory—though it's not supposed to—and this side-effect is not unusual. Hemingway offed himself after losing so much of his memory he couldn't write anymore. Docs claim newer machines or techniques make this less likely, but the evidence suggests it's a scattershot procedure. It is supposed to be used only for depression, a fact ignored by more storytellers than I can count.
Lois and Sheriff Adams see Clark use his powers in "Blank". Luckily, the metahuman he just met can erase the last few moments of someone's memory and he owes Clark a favor.
Said favor being solving his brother's murder after he accidentally wiped Clark's entire memory.
In Freak, Daniel and later Chloe has their memory of Lex's secret lab wiped after being experimented on. After the viewers see the trauma Chloe goes through as Lex's lab rat, it's possibly best for her to forget.
The Haitian from Heroes has the power to erase temporary memories, and at one point someone's entire life history. There's also a subversion as one character suffers major head injuries as a result of his erasures.
Also, in the Season 3 finale, Sylar basically gets his mind rewritten to make him think he's really Nathan Petrelli, after the real Nathan is killed. This being Heroes, there is pretty much no way that this doesn't go south.
In the episode "Spin the Bottle", a spell mentally regresses several characters back to their teens, leaving them with no memories of each other. Angel, upon reverting to his mortal identity as Liam, even forgets that he's a vampire! While the others are upset about waking up in a strange place and being inexplicably aged into adults, centuries-old Angel is more freaked out by automobiles and his sudden lack of Irish accent.
At the end of the fourth season, Angel strikes a deal to magically erase all events related to his son Connor from the minds of his friends and Connor himself. Connor's new, implanted memories are of a suburban human childhood with a Muggle foster family (who also had their memories altered), rather than one spent in a hell dimension as the mortal son of two vampires. It's even implied that the spell retroactively alters reality to support this new history.
In a clever aversion of the standard amnesia plot, when everyone's memories are restored, Connor does not revert to his previous unstable persona. It turns out that a pleasant childhood was just what he needed, and having both sets of memories leaves him with his original warrior skills and a newfound emotional stability.
Although that may have been because he remembers his old life "as a dream", meaning that the usual Amnesiac Dissonance would have much less impact.
Laser guided amnesia is basically the entire premise of Joss Whedon's new show, Dollhouse. They have the technology to erase memories and then give a person Fake Memories, and the show proceeds to demonstrate most of the conceivable ways of abusing it.
Controlled amnesia is the driving plot force in the episode "Needs" (1x08), in which the Dollhouse temporarily erase the memories — but not the identities — of Echo (formerly Caroline), Victor (Anthony), Sierra (Priya) and November (Madeline).
Later, in "Getting Closer" (2x11), Paul rescues November from another Dollhouse in Washington DC and takes her back to Los Angeles, but is allowed to keep her there only on condition of restoring her to her imprint of "Mellie" - the woman Paul fell in love with but deserted after learning she was a doll programmed to spy on him. "Mellie" is restored, but all memory of the breakup is excised to make her trust Paul totally.
Eureka, two episodes: A device that (at first) can erase 20 minutes at a time (hilarity ensues when Carter accidentally shoots Henry and can't remember what happened), and later can erase all memory of an alternate universe.
In Babylon 5, Sinclair's memories of what happened to him during the Battle of the Line were erased by the Minbari after they captured and interrogated him.
Artificially induced amnesia is also used on criminals (called "Death of Personality", the closest thing EarthGov has to the death penalty), wiping their mind and reprogramming them to be upstanding, law-abiding citizens. First referenced in the episode "The Quality of Mercy", and features in the later episode "Passing Through Gethsemane".
On the first season of 24, Teri Bauer escapes from the terrorists, only to get into a car accident and become an amnesiac for a few episodes. This is brought on by shock, as she believes her daughter died in the car wreck.
In the KateModern episode "I can't remember anything!", Kate realises she has no memories of anything that happened that day, the 3rd of August 2007.
In the first season of LOST, Claire returns from her kidnapping with no memories of anything after the season-starting plane crash. (Which was a month or so according to "in-show" time.) The memories came trickling back, and she finally remembered what the Others did to her (which included pumping her full of drugs, making the amnesia a little more realistic).
In Honey I Shrunk The Kids: The TV Show, a memory reliving device causes Diane to forget everything after she was 16, when a power-outage shuts it down.
Episode "Requiem for Methuselah". Spock uses the Vulcan Mind Meld to remove Kirk's memories of Rayna Kapek to relieve his grief over her death. Spock's gesture (literally) is a Crowning Momentof Heartwarming. Perhaps because it's one of the rare instances when Kirk seems truly and deeply affected by the loss (and you get the feeling Spock — at best — has the ability to ease Kirk's pain somewhat, rather than perform a truly Laser Guided procedure). As for other interpretations of the scene: well, those are inevitable...
See also the episode "The Paradise Syndrome", where Kirk's memory is zapped by an alien device, to later be restored by a mind meld with Spock.
Episode "Conundrum". The entire crew suffers from Laser-Guided Amnesia, forgetting who they are, but not their skills. Only the audience knows that the first officer is out of place. This effect is intentional, though, as part of an alien plot.
In a similar episode, "Clues", the entire crew realizes after an unexplained wormhole jump that they are missing one day of memory. Subtle hints suggest that Data knows more about what was going on, but all of the clues lead to a real conspiracy theory. The Enterprise had encountered extremely xenophobic aliens who did not want their existence known. To end hostilities, Picard allowed their memories of that day to be wiped. Data, the only one unaffected by the process, was commanded never to reveal what happened.
A two-part episode, "Workforce", was based on this. Almost the entire crew was captured by aliens and put to work on some planet after having their memories scrambled.
In another episode, some Hirogen capture the ship, suppress almost everyone's memories, implant false memories, and hunt the crew through a variety of holodeck simulations.
A justified example with the Doctor, who, being a hologram, is a computer program. When an experience ends up nearly causing a cascade failure (i.e. total collapse of AI personality), Janeway has his memories of the experience wiped, as well as all the logs. All crewmembers are ordered never to mention it to the Doctor. However, he later starts finding clues, such as a stitch of his own invention that he applied to Harry Kim during this event, or a picture of a crewmember he doesn't recognize. This nearly leads to another cascade failure.
Star Trek: Enterprise did a good episode about anterograde amnesia caused by alien parasites. T'Pol had to tell Archer the whole story again each day for years. Good thing for Vulcan patience.
Used with a twist in one episode, in which a woman who wants to kill her husband gets the amnesia treatment after killing a UFO pilot instead - but the amnesia doesn't affect her desire to kill her husband, and SHADO can't interfere without revealing their secrets.
Liz Lemon's brother on 30 Rock averts part three, having suffered a head injury on a skiing trip that stops him from remembering what happened during and after it. His family is careful to pretend that he'll be leaving for it soon. At the end of the episode Liz exasperatedly shouts at him that he's forty, at which point he appears to snap out of it.
However, given the nature of his injury, it's likely that he would soon forget what she told him.
On Bones, Dr. Brennan suffers from amnesia about the events of a single night. It may have been caused either by drugs or a voodoo curse.
Averted in one episode of Lois and Clark, where a woman uses Jimmy to power her age-reducing machine, and after he manages to run away says that it disrupts short-term memory — so the boy will come home and will wonder how he got there. That's precisely what happens; the next day, Jimmy has no clear memories of a couple hours both sides of the incident.
Charmed has several memory-altering and memory-erasing entities in order to maintain the Masquerade (i.e., the Cleaners and memory dust).
The Doctor Who episode "Journey's End" features a particularly depressing example of this — after becoming overwhelmed by a Time Lord's knowledge, Donna Noble's mind is scrubbed of every single memory of her adventures with the Doctor, undoing all of her character development and restoring her initial self-centered nature and lack of intellectual curiosity. Moreover, the Doctor explains that she must NEVER remember him, or she will die.
Or rather have her head go asplody with an energy discharge that protects her, but knocks everyone else out in a half-mile radius.
In The War Games, Jamie and Zoe are returned to their respective times and have their memories altered so that they don't remember The Doctor as part of his punishment from the Time Lords.
Series 6 introduces the Silence, who have the power to make people forget about them as soon as they look away. Which means they could be anywhere and everywhere...and they are.
in the two-part episode "The Empty Child/The Doctor Dances" Captian Jack cites this as being the reason he left the Time Agents: two years of his life mysteriously deleted.
They also leave you with a post-hypnotic suggestion. The Doctor manages to use their own ability to foil some of their plans by recording a video of one of the Silence saying "you should kill us on sight" and then broadcasting it during the Apollo 11 landing; everybody then starts to unconsciously kill the Silence and then forgets about it.
In Series 7, the entire Dalek species lose their memories of The Doctor.
In the Christmas special, "The Snowmen", the Doctor possesses a worm which erases memory. Just touching it will erase an hour; if it bites you it can erase a lifetime.
Kamen Rider Decade: Tsukasa has this. Subverted as he knows his name, the fact that he is from another world, and recognizes specific people and places in detail.
Averted in Kamen Rider Kiva, in which Wataru finds himself taking care of an Amnesia victim who can't remember his life, but also can't remember basic stuff like how to use chopsticks, what is and isn't edible, or even that fish survive in the water (when we first see him, he's taking carp out of a river to "save them from drowning.") Aside from speaking normally, he's basically regressed back to an infant. This is mostly played for laughs, though.
... at least until we find out he's actually a major villain.
Kamen Rider Zeronos has the power to invoke thison others by simply transforming. The explanation is that his Zeronos cards run on people's memories of himself. After he's done using the card, that person forgets who he is. The Zeronos Cards that enable his Zero Form, on the other hand, wipe out his memories of a certain person.
This also happens to Phillip from Kamen Rider Double, to the point in which he is unable to find anything about his family in his all-knowing Gaia Library. Later on, it's revealed to be an Invoked Trope by the Big Bad.
In Republic Of Doyle, a client loses all of her memories, but can recall names from her past that she used as a con artist.
She does not consciously remember the names but can write them down if she does not think about it and lets muscle memory take over.
One episode of NCIS dealt with a woman who woke up beside a road in a shallow grave and suffered from amnesia. She knew what she liked and didn't like, but that was about it (other than she thought there was an impending attack on a US Navy warship, which caught the attention of NCIS). However, it was later revealed that not only did she make the bombs herself, but she was a member of an agency who built them to test bomb-sniffers and bomb-disposal robots. She blew herself up because, at the end, she finally remembered that the CEO tried to rape her, so she decided to take him down. Literally.
It is heavily implied in the episode "Restless" that this was the reason why the adopted daughter was able to pull off doing a runaway daughter scam thrice (when confronted with the evidence, her reaction indicated that she really didn't know she was doing this until after being brought into questioning by the NCIS). Her uncle, one of the cooks at the second chance shelter, was also in on it, or rather, he was the one pulling the strings.
In The Shadow Line, Jonah Gabriel getting shot in the head caused him to lose his memories of the operation that got him shot, and only these memories. A few characters even note that this sounds suspiciously convenient.
Discussed on The Big Bang Theory after Sheldon tries to teach a lecture. Amy suggests destroying the part of the brain containing that memory with a laser. Sheldon declines.
Happens in the second episode of Chinese Paladin: the hero is mindwiped into forgetting his Call to Adventure—and his vow to protect his new wife. Although he falls in love with said wife again, he doesn't actually recover his memories until near the end of the series.
On Grimm Juliet loses all memories of Nick. She remembers everything else that happened to her but Nick and all things directly related to him have been edited out of all those memories.
Six Hundred Sixty Six Park Avenue: Danielle seems to have her memory wiped regularly for the last sixty years or so, especially after all the times she's been manipulated into killing someone for Gavin.
At the end of the zombie episode of Community, the government wipes the memories of everyone involved. In one of the rare instances of The Tag being plot-relevant, Troy listens to a voicemail from Chang sent during the amnesiac period, bragging about how he slept with Shirley. This raises many questions about the events of the night; for instance, why did he call Troy?
In the Red Dwarf episode "Thanks for the memories" the crew lose their memory of the past four days and try to figure out what happened. It turns out that Lister's "deathday present" to Rimmer of the memory of one of his past relationships didn't work out well, and they all voluntarily erased their memories.
In another episode Holly asked Lister to erase the works of Agatha Christie from his memory banks so he could read them again.
Happens on Dead Like Me if a reaper tries to prove their identity with stories from their past.
On CSI NY, Mac has a realistic version where he cannot recall the events immediately preceeding his being shot. His inability to recall random words and names of places, objects, ect, is a real condition called aphasia, and is laser guided in a sense, but averts most of the usual tropes.
In Infinity Game the previous DM erased all of Trishia's memories (which he created in the first place) and made her Dwarven Defender 00 (D.D.) so she could serve the next Game Master. When Long Wei, the new Game Master, keeps up his DM title so he can enter the game he created, he makes D.D. control the game and forget who the Game Master is so the game is fair.
At the end Long Wei does this to the rest of the team. As the RPG Society are trying to take over the alternative world with their previous game (so the players who were erased could come back - of course, doing this erases the current players, even if they're already dead) they froze the flow of time and the war between the them and Long Wei was slow, if he waited until after the war to bring them back to life and send them to the real world it'd be fifty years in the future. He hopes doing this will mean they aren't traumatised by all the events, but they're all vaguely aware something isn't right.
Both Vampire The Masquerade and Vampire The Requiem have a power called The Forgetful Mind as part of the Dominate Discipline. It allows the vampire to go in and literally rewrite a person's memories by telling them what "really" happened. It's usually used to protect the Masquerade; however, it's made clear that it only really works on more recent memories, and if the account isn't completely comprehensive, cognitive dissonance will ensue.
In Shadowrun there is a drug called laés which erases upwards of a 24 hours worth of memory from the time it's administered. The memories so erased are completely unrecoverable, even by magic.
Dungeons & Dragons has the "Forget" spell as its most basic, and a whole slew of other memory-erasing or memory-rewriting spells from non-core books, like "Forget Past" (Oriental Adventure), "Otto's Tones of Forgetfulness", "Rary's Memory Alteration" (Greyhawk Adventures), "Modify Memory", "Memory Wrack" (Tome of Magic), "Brainkill" (The Complete Book of Necromancers), the psionic science "Mindwipe" (The Complete Psionics Handbook), etc.
Holy slayers (assassins) in Al-Qadim sometimes use a "Blade of Forgetfulness": everyone seeing it swung in a certain pattern suffers a complete memory lapse regarding everything that just happened and is about to happen (up to 3 rounds before and after). Not too hard to guess what sort of events tend to be forgotten this way, is it? Those attacked with such swords are very likely to shake off this effect, but usually this doesn't matter anymore.
The Shadow that transports people, things and beings too monstrous to fall under the people category from undefined fantasy worlds to Earth in the Urban Arcana setting for d20 Modern as a side-effect also strips their memories of any details of those worlds - in effect, they know who they are, but not where they come from beyond Standard Fantasy Setting.
In GURPS Black Ops, the agents of "The Company" have a drug they can slip to someone who has Seen Too Much. They get what seems to be a nasty one-week case of flu, and forget what happened right before getting drugged. The Infinity Patrol from GURPS Time Travel have Eraser, which fits this trope even better — the drugged person blacks out for a bit, and wakes up without memory of the time immediately preceding the drugging. In Black Ops the existence of aliens and monsters must be kept secret, and the Infinity Patrol cannot let anyone know that parallel universes exist.
In Richard Wagner's Götterdämmerung, Siegfried is drugged to forget that he ever met Brunnhilde, but remembers killing the dragon Fafner and all his other early deeds (closely following the plot first found in Völsunga saga). Later, Siegfried steals the Ring from Brunnhilde, but promptly forgets this.
A justified version comes from Another Code, where the Trace has this as one of its functions as a memory control machine. The intent was for it to be used to help remove particularly traumatic memories from people like soldiers or victims.
A perhaps more realistic version appears in Super Robot Wars Advance. One of the protagonists starts off with almost complete amnesia — he can remember instinctive stuff drilled into him, but he can't remember what it's for. His personality is also completely different from his normal personality, and he's noted as "strange" by a lot of the other characters.
In the Street Fighter series, Cammy's amnesia erases all memory of her being a doll of Bison, but doesn't erase her fighting skills. This, despite the fact that she wasn't born, but created simply to be a vessel of Bison's soul.
That's not too hard to figure out. Once a muscle has learned something after doing it enough times, it can become pretty much reflex. And Cammy most definitely used those moves a lot back when she was Killer Bee....
Of course, why would she have any memory of a normal life if she never lived one?
A similar, more recent Street Fighter example of an amnesiac is the French soldier Abel. Much like Cammy in the previous example, Abel is actually a cloned Shadaloo soldier and potential candidate for an alternate body container for Bison. Also parallel to Cammy, Abel is rescued from Shadaloo by a mercenary team.
Planescape: Torment both honors and averts this. At first, the nameless main character can't remember his skills, his identity, or anything about the world he lives in, except the language — a seeming aversion. But as the game progresses, it becomes clear that he isn't learning new skills and abilities, but remembering them; he frightens a hedge witch arguably frightens, since the "hedge witch" is Ravel in a different form by mastering years' worth of magic training in seconds.
People who have recently died in Ghost Trick lose their memories, and recover them again with varying degrees of speed and depth. Sissel forgets not only his identity, but the meaning of many basic concepts such as 'prison cells' and 'science', as well as how to read. Except he hasn't. Sissel can't remember them because he's even forgotten what he originally looked like...a cat, who never understood those concepts in the first place.
In Kingdom Hearts: Chain of Memories, Sora gradually loses some memories and has others rearranged. Recovering them leaves him in a coma for a year, causing him to forget everything that happened while his memories were scrambled. And for some reason, when Sora doesn't have his memories, everyone who knew him doesn't remember him, either! (Although given the way memories seem to work in Kingdom Hearts, this makes a certain degree of sense.) This is clarified in Kingdom Hearts II, where Kairi is barely able to remember that there was a second boy she hung out with. Selphie cannot even recall that there was ever somebody Kairi hung out with other than Riku.
Averted in the beginning of the game. When Sora, Donald, and Goofy forget their fighting skills, they have to relearn them all. Convenient, since the player's also learning a new fighting system. However, Sora's basic combo in Kingdom Hearts II is more precise and polished than in the original game, and according to Word Of God reflects his growing skills as a swordsman, while Donald's magic is visually distinct from Sora's in Kingdom Hearts II, when they shared the same spells in Kingdom Hearts.
Gig from Soul Nomad & the World Eaters has Laser-Guided Amnesia about everything before being Gig (which doesn't really bother him all that terribly, truth be told). He turns out to have once been the legitimate Master of Death of Haephnes, Vigilance. He was slain by Median and his soul was converted into his current form by Drazil, the Dimension Lord of a neighboring world, before being set loose on the world he was once responsible for.
Almost all of the townspeople from Final Fantasy Fables: Chocobo's Dungeon is afflicted with this, due to the influence of the Bell of Oblivion. Trying to remember even the simplest things becomes painful for them, and it's up to Chocobo to dive into their memories and recover the missing pieces.
In Final Fantasy VII, Cloud Strife has a rather severe case of amnesia, due to multiple traumatic events, that led to him wiping his friend Zack from his mind and replacing Zack with himself. Therefore, Cloud, who had been just a common grunt in Shinra's army who failed to make it into SOLDIER, believes he was a SOLDIER First Class and now is a mercenary in Midgar — something Zack told him he wanted to do. He also can't remember anything that happened after he (Zack) faced Sephiroth in one of Shinra's Mako Reactors.
Part of this might have been due to deliberate tampering from Sephiroth/Jenova or a side effect of mako. They appear to be able to tamper with the minds of anyone who has been injected with Jenova cells and mako is supposed to mess with your memories as well. For a while Cloud is not even sure if he is the original Cloud or not.
Not to mention that every Sephiroth clone had had their psyche completely fracture, reducing them to almost mindless puppets. Cloud himself was a mental wreck until he was found by Tifa. It's possible that this huge mental instability added with Cloud's insecurity issues lead to him creating the false 'Zack' persona.
It also doesn't help that Cloud actually does have Zack's memories thanks to the way Jenova cells work.
In Final Fantasy VI, Terra begins the game with almost no memories of her past. Some reemerge quickly, while others do so only slowly. And traumatically.
In Final Fantasy VIIIthe main characters almost all have amnesia which has been caused by the use of guardian forces. With the exception of Irvine who had never used them, all of them had forgotten that they grew up together in an orphanage. Fate still causes them to find each other and work together.
In Final Fantasy IV, Yang washes up in the Kingdom of Baron having lost his memory and so becomes a member of the local guards. He fights the party when encountered and has his memory restored by being beaten, after which he rejoins the party.
I thought he had been brainwashed by Golbez?
The main character of Vagrant Story, Ashley Riot, is a classic example in that while he's an amnesiac about events, he's still the perfect agent. He does start with only basic battle skills, though, and remembers them gradually over the course of the game. It does take a Dark-filled city of the dead to do it, though.
King Varian Wrynn, the hero of World Of Warcraft: the Comic, was kidnapped, cursed to forget his identity and dumped in a hostile shore, so Onyxia, the villain, could rule his kingdom through his doppelgänger.
In Lost Odyssey, Gongora gives Jansen a device to use in case Kaim or Seth recover their memories. Not the first time Gongora ever used them, and Jansen throws it at a guard instead.
Knights of the Old Republic has an important plotline revolving around amnesia. The amnesia is the player-created protagonist's, who is in fact a specific backstory character and not the generic grunt he/she seemed to be. Yes, there are some false memories involved.
It should also be mentioned that this is meta in a quite ridiculous degree, given that KotOR is a role-playing game. It manages to neatly explain how your apparently adult and very capable soldier/rogue/mage doesn't know how to put on clothes or open doors. While it's just teaching you how to work the game mechanics, it has an in story explanation that your memories have been messed with perhaps a little too well.
Happens three times (at least if you're after the good ending) in Cave Story. To injured robots. The third time, Curly actually forgets everything that happened since the last time she woke up with amnesia.
In the new thirteenth ending of Chrono Trigger DS, Anti-Hero Magus attempts to rescue his sister, who has fused with a monstrous entity, and fails. She sends him back to 1000 A.D. with no memory of who he was or where he came from. If this memory loss is meant to be a deliberate act of mercy, it fits this trope; if accidental, it's Easy Amnesia. Either way, it's strongly implied that the amnesiac Magus is Guile of Chrono Cross.
In Xenogears, the Limiter causes an entire planet to forget whatever The Chessmaster Krelian wants them to forget, from history to the existence of entire continents. Naturally, the heroes move to undo this.
The protagonist himself has amnesia thanks to multiple personalities having memories of most of his life before he turned fifteen.
A lot of adventure games exhibit this, simply by not giving the player much information about the setting they're exploring.
The ending of Sly Cooper 3: Honor Amongst Thieveshas Sly forgetting his identity after the final boss fight to his rival Inspector Carmelita Fox, with her telling him that he's actually her Interpol partner and the two escape the island. He later leaves clues for his teammates that he's faking this so that he can pursue a romantic relationship with Carmelita.
Lampshaded in Wild ARMs XF. Early in the game, Labrynthia believes that Clarissa must be Princess Alexia due to their striking resemblance. When Clarissa denies it, Labrynthia hypothesizes that she must have lost her memory in the accident that was supposed to have killed Alexia. Clarissa responds with this gem: "What? That only happens in stories! Real people don't lose their memories that easily!" Later on, it turns out that both Clarissa and Alexia were in an accident at age three, which lead to both of them losing all their memories and being mistaken for each other. So Clarissa really is Alexia with amnesia, just not the Alexia that Labrynthia knew.
Neku in The World Ends With You starts out not remembering anything before him waking up on the Scramble Crossing. It later turns out that Neku's memories were his entry fee, but even then he still has some missing. This is later explained when Joshua, the resident Magnificent Bastard reveals that he'd 'held on' to some of Neku's memories — namely the missing ones, which showed Joshua killing Neku.
In the RPG Hype The Time Quest, the Titular character is turned into stone and sent 200 years in the past. And when he wakes up, he doesn't even know what button to push to draw his sword!
In the end of Mega Man Battle Network 5, Lord Wily does it to his son Dr. Regal. If it weren't for the fact that the former is the series Big Bad, it was just a Shoot the Dog scenario, and an amnesiac Regal loses all of his grudge against humanity.
In the bad ending of Mega Man X 5, this was inflicted on the title character by Dr. Light so the former will not have any memories of Maverick Zero. Furthermore, any information regarding Zero will be rejected by the same programming that erased X's memory in the first place.
Played painfully straight in the campaign mode of Tekken 6, where protagonist Lars Alexandersson has his memory wiped by an explosion in the lab where he found Alisa and it only returns after he squares off against Heihachi Mishima, his father.
Phantasy Star: Any CAST that comes back online after the Great Blank exhibits near-total amnesia. Bodies of CASTs that were terminated beforehand are unaffected, as Ogi demonstrates by taking over two separate bodies. As he explains, the head stores the majority of the actual memory and the entire personality of the CAST while the body holds sub-memory the CAST uses. The amnesia is literally laser-guided, as Mother Trinity employed Photon Noise in an attempt to kill the CASTs that fought against her. The memory damage forced the CASTs offline to prevent total system failure. Those on the moon were purged to a "man", since Mother could not use Photon Noise there without damaging herself. That's not to say she wasn't compromised already...
Appears in Nethack - reading a scroll of amnesia or being successfully attacked by a mind flayer will wipe random parts of the character's memory including any levels which have been mapped. Also the names of items in the inventory will revert to their unknown name state.
Alex Mercer of Prototypewakes up on an autopsy table after having apparently been shot to death. He has no memory of his own identity or why a black ops organization is trying to kill him. Much of the game revolves around his slowly uncovering the truth, revealing that the reason he doesn't have any memories is because he's not Alex Mercer. He's The Virus with a physical body created from Mercer's corpse.
Weiss in Agarest Senki 2 starts off with him killing a servant of a god and a god. He then gets flung out in the middle of nowhere and gets amnesia as a result. He also gets his level reduced from level 99 all the way back down to level 1. And then in a similar fashion as Prototype, Weiss isn't really "Weiss" but instead Chaos aka the god Weiss supposedly killed in the opening! And the real Weiss himself who was the level 99 Weiss actually didn't kill Chaos, but instead got himself killed!
The Conduit: in the tie-in comic book "Orange Lights", The Men In Black use specially-designed orange lights to erase Gordon Well's knowledge of the truth behind the Drudge invasion before he can share it to his listeners.
In Disgaea Hour Of Darkness, Maderas targeted and stole all of Etna's memories related to King Krichevskoy and her promise to him to blackmail her into working for him, while leaving enough information to know they're important to make sure she complies.
Zenon's curse also causes this to every resident of Veldime. They become demons, and start to forget the lives they had before transforming. A couple of the minor characters around town mention the potential Fridge Horror involved; perhaps it would be better to remain demons than to regain their conscience and have to remember what they did while they were monsters.
In Dissidia: Final Fantasy it was heavily implied that the Warriors of both Cosmos and Chaos were under the effect of this trope. This was confirmed in the sequel, and given more explanation: the war between the gods is part of a Groundhog Day Loop that has been going on for several cycles. When a Warrior is summoned into the world, they are stripped of their memories as result of Shinryu's Purification ritual. As the characters fight on, however, they gradually start to regain more memories about their homelands, though the rate varies form person to person. Should a character fall in battle, they undergo the same purification ritual, reviving them for the next cycle but once again robbing them of their memories.
Averted in Tales Of The Abyss: Whatever turned main character Luke fon Fabre into an Amnesiac Hero, after he was kidnapped at the age of ten, wiped him clean: He had to re-learn things such as walking and talking from scratch. The first Plot Twist, which is that he is a clone, also justifies it: since he was decanted during the kidnapping, of course he would not have memories or knowledge. The original he, who is still around, is perfectly functional, except for a serious case of Cloning Blues.
The protagonist of Legend Of Kalevala doesn't remember anything important except that his wolf-like body is an odd piece of work. The main thing he has forgotten is that it's not his body; he's the Brain Uploading replica of a human scientist.
In Fire Emblem: Radiant Dawn, on the second playthrough, Ike regains a piece of his memory Sephiran erased from him to protect him and Mist. As a child, he witnessed his father Greil/Gawain kill his mother and went temporarily insane.
Flashback starts with the protagonist escaping from a base being chased by soldiers. He ends up crash-landing on Titan. He has no memories before that. He also has a holo-cube containing a message of him telling himself to find a friend of his in an underground city. After finding the friend, he plugs you into a machine that restores your memories (at least, up to the moment when they were recorded). They reveal that your character has discovered Aliens Among Us and has developed a device that can detect them. As a precaution, he had his memories recorded and gave the recording to a friend. The aliens kidnapped him, wiped his memory, and planned to kill him. The protagonist has managed to escape, starting the events of the game.
Rodi from the game Shining The Holy Ark suffers this after a cave-in knocks him on the head. It's used to explain away the fact he's forgotten all his skills he displayed in the fight where the player must attack him. Eventually his memories and skills come back as you play through the game.
I Miss The Sunrise has Ros, who can remember everything except what happened before s/he was put in stasis.
Anyone can have this, actually, and it is a necessary side effect of immortality; Typelog has devised a system allowing people to replace unused memories with ones they currently need.
Played with in Snatcher, where Gillian Seed and his wife, Jamie, remember nothing about who they are or where they come from, though they somehow find out their names and the fact that they are married.
In Fallout 3, Dr. Zimmer's escaped android A-321 has undergone a memory wipe via circuit neuralizer, along with Magic Plastic Surgery courtesy of Dr. Pinkerton and renaming himself Harkness.
In Ib, the dolls inflict this on Garry if he fails their little game, causing him to forget what he learned about Mary. It doesn't last though; Mary attempting to knife him jogs his memory.
In addition Kotarou starts the main story with this.
In Duel Savior Destiny for the resolution of Mia Touma's route, she has her memories wiped at the end so that she doesn't have to bear the weight of events that occurred in her story line.
A justified version comes from Another Code, where the Trace device has this as one of its functions as a memory control machine. The intent was for it to be used to help remove particularly traumatic memories from people like soldiers or victims.
In Fate Stay Night, Heavens Feel route, Shirou gets a form of anterograde amnesia when he loosens the binding on Archer's arm. It becomes more typical retrograde amnesia later on.
Shiki in Tsukihime had his previous memories of his life among the Nanaya clan magically erased by Makihasa after his incident with SHIKI. In fact, he doesn't even remember they existed for the most part and initially thinks of himself as SHIKI, the real son of Makihasa Tohno. Later, Akiha informs him that his memories cannot be replaced and that all records of his previous life were destroyed years ago. But he doesn't really care.
In the visual novel True Remembrance, destroying memories is used as a method of treating depression.
In Eien No Aselia before the story started Yuuto made a Deal with the Devil to save his little sister. The game starts when the devil in question (a sentient weapon) forces him to complete the contract and at the same time restores his memory of having made the deal. Later, Tokimi wipes his memory again when said sword is destroyed and he is rendered unable to fight.
Averted in Miamaska: Amity suffers a concussion and has memory problems of what happened for the next six days. She still has fuzzy memories of what occurred beforehand, though.
Funny Farm: Mavis forgets two years of her life thanks to a time bomb subconsciously implanted by a cult hypnotist. Later, Boe gets short-term amnesia from an explosion, causing him to forget what happened just prior, including his realization of his love for Mileena. Eventually, he remembers that there was some sort of love confession, though the details are fuzzy. The trope's subverted when it's revealed that the apparent amnesiac is not Boe at all, but Orwell pretending to be Boe and using amnesia as an excuse to not remember specifics.
After Wanda finishes interrogating Jillian in Erfworld, the guard comments on the "fascinating" things he overheard and tries to ask a few questions. Wanda tosses some magic powder in his face and tells him, "You heard only the screams for mercy."
The Oracle of The Order of the Stick has a charm on his valley that prevents supplicants from remembering anything of their experience there, other than the answer they received for their questions. Among other things this keeps it unknown that the Oracle is a mere kobold, who is less than helpful to his customers. Roy (in ghost form) is able to bypass this when he is banished from the valley back to the afterlife.
Also, after his resurrection, Roy cannot remember well any of the time he spent in Lawful Good Heaven (though he remembers the pre-Heaven limbo).
In Freefall, Ecosystems Unlimited owns several anti-memory devices, each with a specific purpose, including retrograde and anterograde amnesia. Justified as Bowman's Wolves' brains were designed to react to those devices.
Only the retrograde amnesia is targeted, the anterograde amnesia is general.
In Errant Story, when the elf Sarine has some emotional memories of her human husband and half-elf child come up one night, her human traveling companion Jon confronts her. Impulsively, she jumps him. The next day, when he awkwardly tries to bring it up, she casts a memory charm on him, leaving him deeply distrustful of her. He can tell that his memories were manipulated somehow, and whatever was removed, he assumes, must have been far worse than a one-night stand.
Earthsong features this trope on any character arriving there, due to the transport process. They still have a "remnant," a memory of the last thing they did before being transported to Earthsong. The two known exceptions to this pattern are Nanashi, who remembers everything of her past life after having wielded the Sideran weapons, and Willow, who doesn't even have a remnant. Considering that Willow is Earthsong's Eve, she probably never had a memory to lose yet.
Jigsaw in Last Res0rt has a relatively realistic bout of amnesia surrounding how she became a vampire. To complicate matters, she then apparently proceeds to feed in her sleep, allowing her to go for almost three months before Daisy actually has the presence of mind to just TELL HER she's a vampire.
In Sluggy Freelance, the Harry Potter-style wizards have the Forgetyoubliviate spell for this. It's used to erase Torg's memories of Hoggelrynth, and one inadvertently erases everyone's memories of Millard Stoop.
In Fleep, the amnesia is so laser-guided that the affected character doesn't even realize he has amnesia (at first). He walks into a phone booth in San Francisco; several years later, he wakes up inside a phone booth on a completely different continent—and with no memory of the intervening events, he thinks he's still in that booth in California.
Mixed Myth actually came up with two clever explanations for why the Sphinx Tamit can't remember anything besides her name. Her first explanation is that, since she's immortal, she has to periodically remove her memories with magic to prevent being overwhelmed. It's eventually revealed that this isn't true, and that she's the Anthropomorphic Personification of Mystery, so she's cursed to be a mystery to herself—remembering her true identity triggers the magic that causes her to immediately forget everything.
Several varieties of this exist in Blip: both witch spells and vampire breath are capable of erasing memories. K also has dream amnesia, where she regularly has lucid dreams, but can only remember them as she's dreaming.
In Gunnerkrigg Court, Coyote removes the memory of Ysengrin's insane attack on Antimony from his mind, against his will. This apparently isn't the first time this has happened, by far.
In the FanWebcomicverse called the Building-verse both Aziraphale and Crowley (Girls Next Door) and Jareth (Roommates) can do this but in different ways (the former two mind wipe you the later manipulates your time perception the effect is quite similar) and success rate (Jareth failed once). Both comics played with and lampshaded the dubious morality of this.
Off-White has a self imposed example. Iki deliberately forgot his life as Skoll, the sun chaser. It took a encounter with his brother Hati for him to remember.
The Alpha AI introduced to viewers in Red vs. Blue: Reconstruction deliberately severed its memories from itself some time ago as a coping mechanism for the torture inflicted upon it by Project Freelancer. Those severed memories formed the Epsilon AI, which merely "suppressed" them (after going insane for a period).
The Operator seems to affect people this way in Marble Hornets. Sometimes it's a result of meeting him directly, other times it can happen just from being in the same area as him - Jay had completely forgotten being involved in the student film that started the plot. "Part 2" opens with the biggest example yet: Jay wakes up in a hotel with no memory of anything during the seven-month gap between entries.
The Agents of LIS_DEAD are all mind-wiped from their parents' memories, from the memories of all their parents' family, and from all the surrounding community and records. From birth.
If a Brown Note has only mental effects, there's a good chance the victim can be cured simply by erasing all memories of being exposed to the Brown Note.
The Foundation has SCP-055, "the Self Keeping Secret". As soon as anyone walks out of the room containing SCP-055 they forget any facts about it; same goes for looking away from a photo of it. No one can even remember that they're in possession of an amnesia inducing entity: Foundation personnel will frequently come across the SCP-055 database entry, freak out about the fact that there's an unknown entity right inside their base, and then promptly forget about it.
Furthermore... wait, what were we talking about?
On two occasions in Funny Business, Jeannette erases an event from her parents' memories. Both instances being rather traumatic for all involved, she rationalizes this behavior as being for the best, even though she doesn't like using her powers on other people.
The events were only erased up until Danny took the test it seemed (Jazz is still outside the room, waiting to catch Dark Danny but stops when she sees it's the real one in there).
Chip N Dale Rescue Rangers had an episode where the Rangers were traveling in France and Dale suffered a blow to the head, whereupon he completely forgot everything about himself and his friends, including his affinity for Hawaiian shirts and practical joking. He was found by a French doppelganger for Fat Cat who turned him into his own personal super-soldier, Ram-Dale. Hilarity Ensues when he finally catches up with the Rangers and tries to kill them. In the end, another blow to the head restores his memory.
Kim Possible avoided this in the episode "Clean Slate", in which Kim has amnesia, and is pretty much square-peg-round-hole retarded until they manage to restore most of her memories.
Parodied mercilessly on Futurama whenever Calculon and the cast of All My Circuits take the stage.
Also played somewhat-straight in "The Why of Fry," when Nibbler wipes Fry's mind clean of the Brainspawn incident.
In She Ra Princess Of Power, it's stated that after baby Adora was kidnapped by Hordak and taken away, the Sorceress erased the Eternia people's memories of the missing Princess; only King Randor, Queen Marlenna, Man-At-Arms and the Sorceress herself know the truth. But then, that's Magical Amnesia for you.
In Code Lyoko, Aelita has no memories of her life before the Supercomputer was turned back on and she woke up on Lyoko — including the fact she was human, thus she's belived to be an A.I by everyone including her. It is revealed at the end of Season 2 that XANA had stolen those memories, and uses them to link Aelita's life to the continued working of the Supercomputer.
Also, in Season 1 episode "Amnesia", nanomachines created by XANA are causing memory wipes typical for this trope, affecting Ulrich among others.
In an episode of Gargoyles, an alien uses his advanced technology to induce temporary amnesia in Elisa with the intent of erasing what he believes are her false memories of the Gargoyles as her friends (she is told that her true memories will return in a few days). Elisa is then understandably freaked out by her first post-mindwipe encounter with Goliath. Fortunately, her gun wasn't loaded when she pulled it on him. This in turn is the key for Goliath figuring out that something is wrong with Elisa's memory, as she not only didn't recognize him, but she also didn't know her gun was empty, a condition that had existed for at least a month in-story at the time.
Also, Puck's first appearance where he eventually reverses the entire city's human/gargoyle status. Everyone thinks their current body is the one they've always had, but all their other memories remain intact and our heroes quickly figure out something is up just by logical reasoning, like the former gargoyles remembering being able to fly and humans-turned-gargoyles insisting they can't despite having wings.
Captain Hero from Drawn Together appears to be able to do this by stripping unconscious bodies and violating them.
Jorgen Von Strangle of The Fairly Odd Parents often uses this to erase kids' memories when they reveal the existence of their godparents.
As the main character, Timmy Turner would never lose his fairies, so this is used to erase the memory of his friends and family in every episode that, for some reason, he is forced to reveal his fairies existance (most of the times in an attempt to save them and defeat the Big Bad).
Parodied in Family Guy when Lois used the neuralizer on Chris when he doesn't stop saying "boobies" after the Griffins visited the nudist family's house.
Burns: Fiddle-faddle, everyone knows our mutants have flippers. Oh! I've said too much. Smithers, use the amnesia ray. Smithers:You mean the revolver, sir? Burns: Precisely. Be sure to wipe your own memory clear when you've finished.
Also invoked by Homer in one episode, who wakes up with no memory of only the night before because he drank a special cocktail that erased the last 24 hours from his memories so he could forget the planning his family was doing to create a surprise party for him.
Generator Rex has a chronic variety of this. He's lost his memory several times in the past, for reasons that probably relate to his powers. Why this keeps happening has yet to be explained.
In "Six Minus Six" Agent Six loses six years of memory saving Rex from a machine that was going to delete Rex's instead (because Rex apparently goes crazy if he resets, and if that happens Six has to kill him). It has so far not been fixed via Reset Button and might not be. That means not only does he not remember Rex, Holiday or Bob, but he doesn't rememeber White Knight or even the Event that caused the EVOS (heck, he barely knows what an EVO is). He only stayed with Providence and is trying to be the man he used to be because of Rex's unwavering trust him, even as he was six years ago (an unrepentant, mercenary Jerk Ass).
In Dexters Laboratory, Dexter is shown erasing his parents' memories of his lab after enlisting their help in defeating a giant monster in the presumptive Grand Finale. Later, his pet monkey erases Dexter's memory of monkey's superpowers. In an earlier episode, Dex accidentally says that he has a lab, prompting Dee Dee to respond "Smooth move, Dexter. Now you'll have to erase Mom and Dad's memories...again!"
Happens in the Young Justice episode "Bereft", where villain Psimon psychically attacks Miss Martian, erasing her memories for the past six months and also erasing everyone's memories of the past six months too since they were all mentally connected with Miss Martian at the time. This leaves Superboy a mindless berserker, Artemis and Megan strangers to everyone else and Robin, Kid Flash and Aqualad ignorant of the mission.
In TRON: Uprising, it's established that any program who loses their IdentityDisc starts having a glitch in the form of temporary bouts of memory loss, and eventually becomes a 'stray' - unable to hold any long-term or short-term memories, and even unable to have a notion of 'self'. Unfortunately for Beck, he has his Disc nicked in the episode "Identity", and is almost tricked into going with the Military before he gets his disc back.
In Codename Kids Next Door, this is standard procedure for operatives that retire upon turning thirteen years old. (Referred to as "decomissionig".) This is not without justification, seeing as those who have refused the proceedure and escaped (such as Numbuh Five's sister Cree) have become some of their worst enemies. The process can be reversed, however, as it was in "Operation: Z.E.R.O." Another episode reveals that not every operative is decomissioned at age thirteen. Some, like Maurice, act as deep-cover agents who are still loyal to the K.N.D. despite not being kids anymore.
A common side-effect of the so-called "rape drug" sedatives Rohypnol and GHB (gamma-hydroxybutyrate) is retrograde amnesia, covering the time span the victim was under the drug and usually a short while previous to ingesting it.
Likewise, imbibing heroic amounts of alcohol can induce retrograde amnesia — GHB shares many of the biochemical processes, but is far [more?] rapid in effect, which is why it's such an insidious thing to spike a drink with.
All benzodiazepines (i.e. drugs in the Valium family, of which Rohypnol is one) can potentially cause retrograde amnesia, but some more than others. Doctors and dentists sometimes deliberately choose Ativan (lorazepam) for its strong tendency in this direction, which makes it ideal for sedating patients prior to unpleasant procedures. Some things you'd be thankful not to recall in great detail.
Ketamine, an anisthetic drug used in Veterinary medicine, causes amnesia from onset to awakening. This makes it very useful for use in animals (it's hard to treat an animal who has a subconcious aversion towards you after they've been under), but also makes it very illegal to handle without supervision of a liscenced veterinarian.
Many severe accident victims lose memory of the accident as a result of the trauma. Memories don't quite form instantly, so if something happens to interrupt your brain's function (such as your head slamming into the pavement) the memory of the event will never have a chance to form in the first place.
And of course the whole repressed memory thing, where the mind blocks out painful memories so we're only disturbed on the subconscious level. Though the nature of this and even whether or not it exists is controversial.
There's an English soccer player called Mills who spent the night in his rival player's house after getting hit on the head. He very specifically couldn't remember the events of the match in which the accident happened... or what team he played for. Everything else was absolutely fine. Fortunately, this didn't last long.
Daniel Agger of Liverpool got a nasty concussion during the tie with Arsenal this season. He says he doesn't remember the match at all. Which considering Reina's dicking it up at literally the last minute it probably a good thing.
Same with the time when John Terry was knocked out after being kicked in the head against Arsenal (who seem to have a thing about causing head injuries) a couple of seasons back, he apparently couldn't remember anything that happened after coming out the tunnel for the second half: http://www.youtube.com/watch?v=8GEB-TYLMmQ
In the wake of the infamous "wilding" outbreak in Central Park in April of 1989, Trisha Meili (then referred to only as "the jogger" to preserve her privacy) was found unconscious and near death. She was unable to testify against her alleged attackers in court, as repeated blows to the head had left her unable to recall anything of the assault, or indeed any event between arriving home from work that afternoon and awakening in a hospital six weeks later.
Stephen King wrote Cujo during his drinking days. He vaguely remembers writing the book, but only the Broad Strokes of the process. He can't remember the specifics or how he came up with what he feels were the best parts of the story.
Unsolved Mysteries once had an amnesia story where a man shows up in a town with absolutely no memory of his past or identity. A man gives him a job, and a customer came in and realized that he was operating an old-style adding machine so efficiently that he must have worked on them professionally in the past, which they used as a first step in figuring out his identity.
A woman who had an accident and lost several years of memory, including that of her husband, was the inspiration for the film The Vow.