A new character appears in a work part-way through, but for some reason the established characters don't notice and treat them as if they've always been part of the team or community. Sometimes, they may even discuss the character's involvement in past events which the audience knows that they didn't play any part in.
The reason is some kind of in-universe SF or fantasy phenomenon. Common examples are Fake Memories, where the characters' memories have been altered without actually changing the past, or outright Reality Warping, where the timeline has been forcibly altered to insert the new character. At times this may be a particularly visible effect of a larger-scale Cosmic Retcon.
This is usually a villainous move, as changing people's memories or whole pasts without asking them can seem like a violation. Sympathetic characters who do this are often suffering from Power Incontinence, and may even be unaware of the truth themselves.
Inversions are also known, where a character genuinely did exist in the past, but some kind of phlebotinum previously prevented the other characters, and presumably the audience, from noticing or remembering them.
Not to be confused with Remember the New Guy?, where a new character is introduced as if they have always been around somehow in the background or just off-screen, and the audience is expected to simply accept it, because the writers couldn't be bothered to write a proper character introduction for them. Many examples of this are, however, intended as parodies or deconstructions of that trope. Compare the difference between The Nth Doctor and The Other Darrin. A type of Revealing Continuity Lapse.
Since this is almost always a massive spoiler, no spoiler code will be used in examples. Consider yourself warned.
- Bleach: Mr. Tsukishima has this as a power. He did a Remember the New Guy? on near everyone Ichigo knows, as part of a gambit to confuse Ichigo into handing over his life. By adding details, he can do things such as change the environment, learn about others, or make them collapse from the stress of conflicting info.
- Rolo Lamperouge from Code Geass manages to insert himself into the main cast between seasons 1 and 2. Specifically, he is supposedly the main character Lelouch's little brother (replacing the sister he had previously, Nunnally). He's really an assassin who has been appointed with the mission of keeping watch over Lelouch, after the Ashford students are given Fake Memories and an amnesiac Lelouch is sent there as well, to keep him out of the way of The Emperor's plans. It doesn't work.
- In Fairy Tail, when Master Makarov selects the candidates for the S-Class exams, one of them is Mest, a character we have never seen before, yet everybody claims he is a valued Fairy Tail member. He is a spy who inflicted Fake Memories on everybody. And then, hundreds of chapters later, he is revealed to be a Fairy Tail member from the beginning who even erased his own memories to spy on the Magic Council.
- Yashiro Isana in K is an interesting example in that even he remembers having been there all along. By the time of The Reveal half way through the first season, everyone who was made to Remember The New Guy has forgotten him, which is what leads him to realize his memories had been tampered with. Everyone in the school not only remembered him, they loved him enough to eagerly share their food with him every day.
- In Majokko Meg-chan, Meg is a young witch who has been sent to Earth where is adopted by former witch Mami Kanzaki. In the first episode, Mami bewitches her husband and their two children, Rabi and Apo, into believing that Megu has always been the eldest child of the family.
- Puella Magi Madoka Magica the Movie: Rebellion does this with Bebe a.k.a. Charlotte/Nagisa, Mami's pet witch. Mami claims to have adopted her long before meeting Madoka and Sayaka, and that they were inseparable ever since; but Bebe appeared only briefly in the original series, when she literally bit Mami's head off, and then got blown up by Homura. She was never Mami's pet before the movie, but none of the characters can remember her being anything else. It turns out that Homura has manipulated the memories of most of the cast, including herself, and "Bebe" is only the tip of the iceberg.
- s-CRY-ed pulls an interesting version of this in regards to Ryuhou in the second half, after he's lost his memories and his former organization tracks him down. While he was implicitly already familiar with Kigetsuki's Alters, a trio of almost-entirely-human beings called the Tokonatsu sisters, Unkei forces this trope on him by using his Alter, Mad Sprict, to implant false memories within Ryuhou and make him believe the Tokonatsu sisters were all his fiancÃ&A Elig;ÃÂ©es since childhood - complete with revisiting earlier flashbacks to Ryuhou's childhood when he first met Mimori, but with one of the three Tokonatsu sisters taking Mimori's place in the different flashbacks. Ryuhou is definitely not pleased when his memories actually return.
- Tenchi in Tokyo: Sakuya Kumashiro was created by the Big Bad Yugi and inserted into the school Tenchi goes to in Tokyo, with all her classmates getting false memories of her. Since Tenchi was new in town to begin with he never had the opportunity to even suspect anything was different. Ultimately, once Yugi decided that Sakuya had outlived her usefulness, Sakuya was reabsorbed back into her and all the other students besides Tenchi forgot she'd ever existed- she even disappeared from photographs.
- Yu-Gi-Oh! GX: Season 4, where the characters are shown instantly treating the previously unknown Yusuke Fujiwara like he's one of the True Companions all along — because he's hypnotized them into thinking so. Too bad his magic doesn't work on Judai. It doesn't work on Fubuki, too, because Fubuki knew Fujiwara already.
- In Adventure Time, Finn and Jake destroy a magical statue and then discover that they now have an adopted sister, Gata, who is intimately familiar with everyone they know and has apparently lived with them for years. Gata was once actually their sister, but their father magically banished her to another universe and removed all memories of her existence after discovering she was an Apocalypse Maiden that created a portal to a dimension filled with powerful demons when she slept. The statue was the seal to that universe, and destroying it restored her to theirs. At the end, Gata decides to perform a Heroic Sacrifice and re-banish herself and the demons (who are led by her birth mother). Finn and Jake instantly forget about her when she does so. This gets a Belated Happy Ending at the end of the "Dungeon Master" arc, where the defeat of the villains of that storyline somehow strips her birth mother of her powers and allows Gata to safely exist again.
- Archie Comics' Sonic the Hedgehog: Following the Cosmic Retcon (and real-life lawsuit) induced Continuity Reboot, numerous characters have shown up who have histories with the preexisting characters that are completely new to the audience. Possibly lampshaded in the case of Breezie the Hedgehog, whom Amy points out Sonic and Tails have never mentioned to the rest of the team before.
- This seemed to happen with Moonraker's sudden appearance in Force Works. Everybody knew him and he even was in an ongoing relationship with Spider-Woman. However, Rachel (Spider-Woman's daughter) notices she had never seen him before. Some issues later, Moonraker reveals he was really implanted into the team's history via time travel to warn them and the Avengers about an upcoming attack by Kang.
- A major plot point in the Avengers: No Surrender crossover involves the return of Voyager, a former Silver Age Avenger who was supposedly lost in time after a battle with Squadron Sinister. It's eventually revealed that Voyager is really the Grandmaster's daughter, and that she used her powers to infiltrate the team by worming her way into everyone's memories, thus making them all believe she was a founding Avenger. She eventually does a HeelFace Turn and restores everyone's memories voluntarily.
- Batgirl (2011) introduced Babs's old schoolfriend Greg, who turns out to be a memory-warping villain called Fugue, who Babs had never met before
- One of the Fear Itself tie-ins to Secret Avengers introduced Leonard Gary, a friend of Beast's with Omega-level Reality Warper abilities. Leonard is shown to be so powerful that he literally brings Washington D.C. to life to repel Red Skull's Neo-Nazi invasion, and yet we've never heard of him before. It is however justified since Beast implies that Leonard deliberately used his powers to hide himself from people like the X-Men..
- In the Transformers tie in mini-series of the IDW comics crossover event Infestation, Galvatron has his loyal crew of Cyclonus, Scourge and... Bayonet, a female helicopter transformer we've never seen before and is part of the crew. She is the Big Bad Britt, disguised as a transformer who used her powers to mess with everyone's memories to make them all believe that she was there all along. Kup, who's going crazy by this point, is the first to notice, and when trying to write it off as paranoia fails, she impales him.
- In X-Men: Legacy, Forgetmenot's mutant power made people forget his existence the moment they stop actively thinking about him. He's apparently been an X-Men for six, in-story years.
- In the short-lived Rogue solo series, Blindspot was retconned into being a friend of Rogue and a member of the Brotherhood, but since she has the power to manipulate memories, she was able to erase all knowledge of her existence after going into hiding.
- DC's Moon Maiden and Triumph, and Marvel's The Sentry. All three are modern characters retconned as heroes from the Silver Age who happened to save the world in a way that erases everyone's memories of them. Leading up to the series that introduced the Sentry, Marvel got comic news sources in on the joke; they ran stories about how he really was a Silver Age hero who was created back then but never used and promptly forgotten. Nor was this the first time Marvel had tried this tactic. 3D-Man was made in the Seventies but his story had him as active since the Fifties. There was even a What If? story where he was present as a founding member of a 50's version of The Avengersnote .
- My Little Pony: Friendship Is Magic fan works have done this a few times to lampshade the canon's heavy Remember the New Guy? tendencies:
- In Pony POV Series:
- It is eventually revealed that Shining Armor literally didn't exist before he was introduced, and once he appeared, the timeline adjusted itself both past and future to accommodate him. When he finds out, it's a Tomato in the Mirror moment for him.
- During the Finale Arc, Button acts like he's always been Sweetie Belle's coltfriend and the Crusaders' Sixth Ranger. However, this is because from his perspective, it really had always been that way.
- Also during the Finale Arc, Maud Pie is really the amnesiac avatar of Entropy, the Goddess of Nothingness and Endings. Upon her arrival, characters briefly question who she is before their memories are rewritten so that they believe she is Pinkie Pie's older sister. As Maud doesn't remember being Entropy and only remembers being Maud, she genuinely believes she is Pinkie Pie's older sister.
- BBBCF explains why Cadance and Shining Armor suddenly appeared at the end of season 2 by making Shining Armor a newly spawned changeling drone, with the whole wedding a contrived excuse to distract Chrysalis from Cadance's importance.
- In Den Fjerde Vaeg, some force from another universe is altering the past to insert new characters, and altering everypony's memories to match. Only the ponies with fourth wall awareness retain Ripple Effect-Proof Memory. When Maud Pie pops into existence, Pinkie is a bit disturbed at suddenly gaining an older sister. When Twilight Sparkle learns of the fourth wall, she abruptly regains memories of being an only child, from before her older brother Shining Armor was retconned in.
- In Pony POV Series:
- In Harry Potter and the Natural 20, Milo is a Munchkin with the standard Dungeons & Dragons Player Character ability to add details to his backstory at will. So naturally, he exploits this trope for all its worth.
"What did you do?" Relkin asked in a hushed voice.
"I remembered each and every one of them as a treasured friend or relative from my backstory," Milo said quietly. "One who would never, ever raise a hand against me or impede the cause of Justice or the furthering of Good. And who gets +2 and a reroll against magical orders against their nature."
- In Long-Term Memories, original villain Spinel replaces Garnet and imposes fake memories on the other characters so that they believe she's always been there instead of her.
- Late in Perfection is Overrated, Bachiko is introduced as a supposed childhood friend of Mai, and it's claimed that Mai has also known Bachiko's best friend Meiko when she first arrived at Fuuka, in a manner similar to the Mary Sue examples listed above. Natsuki is confused when Mai and the others assume she knows the two when she knows she doesn't. It turns out that Meiko, using her powers, altered everyone's memories so that they would remember herself and Bachiko as their friends, as part of an Evil Plan to manipulate everyone's relationships as they see fit with Bachiko's personality altering abilities, and they posed as Mai's friends in order to monitor their progress. Natsuki happened to be outside of Fuuka's campus at the time, and so was not affected by Meiko's power.
- Done In-Universe in The Vampire Diaries story "Return to Mystic Falls" by Elena who is really Katherine. She had a witch make people think she had been there all along to fool people, especially Stefan.
- Men in Black 3: After Boris alters the timeline by going back to 1969 to kill K. J gets on the elevator to go to work and he is joined by another agent, AA, who addresses J as if J is his partner. Neither J nor the audience has ever met this guy before, much less been partnered up with him. J naturally knows something's wrong.
- In Grinny by Nicholas Fisk, the title character has this as an explicit power: by saying "You remember me", she can make adults (but not children) think they've known her all their lives.
- Percy Jackson and the Olympians
- In the series, the Mist can be manipulated to create Fake Memories of a person. For example, after Mrs. Dodds (Percy's teacher and a servant of Hades) attacks Percy and is killed, a new teacher named Mrs. Kerr mysteriously appears to take her place, and nobody but Percy remembers that Mrs. Kerr hasn't always been their teacher.
- This is also used in the Sequel Series, The Heroes of Olympus, to get Jason's classmates to think that he has always been in their class. Leo Valdez believes that Jason was his best friend, and Piper McLean even has memories of dating Jason.
- The Torchwood novel Border Princes by Dan Abnett (published between series 1 and 2) has pretty much exactly the same plot as the episode "Adam" (below), except it's a Reality Warper, rather than a memory-alterer, and he isn't doing it intentionally.
- In Angel, Connor inverts the trope by being given fake memories of a normal life, so that no one except Angel and Cordelia remembered his true identity. The Beast's introduction also has shades of this, because Angelus remembers him but Angel (and thus the audience) doesn't.
- Buffy the Vampire Slayer: One of the most significant examples is the case of Buffy's little sister Dawn, whom everyone treated as always being around despite only debuting in the fifth season. She actually didn't exist before her first appearance; she's really a cosmic key between dimensions, transformed into a human being in order to hide her from a demon goddess. The monks who transformed her also created memories of her in everyone's minds to ensure that she has the Slayer to protect her. The trope goes far enough that Dawn is referenced on Angel, the spin-off show she never appeared on, because Angel himself would have met Dawn in the first season of Buffy. She also appears in comics and novels set before the fifth season, on the grounds that the characters would have remembered her being there even though she wasn't there before. When a Buffy animated series, set during their high school years, was in development, Dawn was planned as a main character.
- The Flash (2014):
- In season three, various alterations to the timeline result in (among other things) Barry having a new co-worker at Central City forensics. Barry is the only one with Ripple Effect-Proof Memory, so only he finds this odd.
Barry: How have I been working with this guy for a year?
Joe: You say that all the time.
Barry: I'm sure I do!
- When Professor Stein visits during the "Invasion" crossover, he discovers that, due to advice he gave his past self on his own show, he has a fully-grown daughter with an entire life story he doesn't remember.
- In season three, various alterations to the timeline result in (among other things) Barry having a new co-worker at Central City forensics. Barry is the only one with Ripple Effect-Proof Memory, so only he finds this odd.
- Parodied in Scrubs. New character Kim Brigs is introduced as a new character, only for Turk to explain to JD that she's been at the hospital literally as long as they have. A montage ensues of Kim composited into scenes from earlier seasons where she wasn't actually there. The excuse for this? Women wearing wedding rings are literally invisible to JD.
- Stargate SG-1: The episode "The Fifth Man" starts with SG-1 having to leave Jack and new member Lt. Tyler behind as they flee a bunch of Jaffa, when they get to the SGC and say that Tyler was injured Hammond says "who?" Tyler eventually comes clean that he's an alien who secretes a pheromone that makes one perceive them as a familiar (even if fictious) figure they have always known. Since he was running from their mutual enemies they let him go. In later episodes, they use the memory-altering compound to infiltrate enemy organizations.
- Star Trek: The Next Generation:
- Possibly the first lampshaded use of this was during episode "Conundrum". The entire crew is hit with amnesia and forget their ranks. The executive officer, MacDuff, is someone the audience has never before met. Turns out he is an alien intruder, trying to trick the Enterprise into attacking the enemies of his species.
- Played with in Tasha Yar during the Alternate Timeline in "Yesterday's Enterprise", where she insists she's always been good friends with Guinan. Guinan, of course, never met Tasha and thanks to her species's Ripple Effect-Proof Memory, instinctively knows this is untrue.
- Quite a clever example appears in Star Trek: Voyager when the EMH finds evidence of crew member Ahni Jetal who he cannot remember ever being on Voyager. It turns out that his memories of her were deleted when he failed to save her life, an event too traumatic for his programming to take. Considering that she really had never appeared on the show before, a possible reading is that the entire series up until that point reflects the EMH's edited memories, and Jetal could have been around and involved in major plot points.
- Torchwood: "Adam" is all about this. Gwen enters the Hub one day to find a New Guy working like he's been there all along. She's never seen him bef- Oh, wait, of course she has. The New Guy is actually an extra-dimensional entity that implanted himself into everyone's memories because he has to be remembered to exist. They even did a Special Edition Title sequence that implanted the mysterious new guy.
- "The Lateness of the Hour", an episode of The Twilight Zone. A wealthy, reclusive couple's android servants have implanted "memories" and are programmed to believe that they have been in their positions for years. All hell breaks loose when the couple's grown daughter figures out that this applies to her too.
- Inverted in The X-Files episode "The Lost Art of Forehead Sweat", about various false memory syndromes including repressed memories and the Mandela Effect. Reggie, the guy who tells Mulder and Scully about the memory conspiracy, insists he's known them for years, and eventually claims to have founded the X-Files, but nobody apart from him remembers this because he's being erased. He turns out to probably just be crazy. Or is he?
Skinner: Hey, where are they taking Reggie?
- Invoked and lampshaded in Fire Emblem Fates. Hidden Truths reveals that Anankos's good side had actually given false backstories to Inigo, Severa, and Owain when he took them to his world. Since their backstories involve them having earned enough of a reputation in the world to serve the royal family, it's implied that Anankos possibly warped peoples' memories around to account for their presence in the world. Xander, however, points out in his C support with Laslow that he does find it odd that he has never even heard of Laslow before he was appointed as his retainer, but he will not question the results.
- Niles provides an additional lampshade in his supports with Selena, pointing out that they may as well have appeared out of thin air before they started serving the Nohrian royal family.
- In Kingdom Hearts: Chain of Memories, Sora is subject to Castle Oblivion's memory-altering shenanigans, and as he slowly loses some memories, others that he had forgotten come back to him. Through this, he's reminded of his one-time friend Naminé, and as time goes on, he speaks of Naminé more and more, even though she did not appear in his hometown in the first Kingdom Hearts and was never mentioned previously. Eventually, he manages to completely forget about his actual childhood friend Kairi, whom Naminé seems to have supplanted in his memories... and there's actually good excuse for all this! He didn't really know Naminé when he was younger, and the Castle's supposed powers were a ruse; Naminé was being coerced by Organization XIII into using her unique ability to tamper with Sora's memories in order to serve their own interests. This was probably made easier by Naminé being Kairi's Nobody.
- We actually see the final stages of this process early in Tsukihime, as Ciel completes her integration into Shiki's school community, and he has trouble "remembering" her at first, until she "reminds" him of their previous meetings. In reality, Ciel is an agent of The Church who has arrived in town to pursue an ancient vampire connected to Shiki's family, so she has been using magic to insert herself into his and his classmates' memories.
- In Season 5 of The Adventures of Puss in Boots, the episode "The Iceman Melteth" suddenly features a new orphan, Li'l Pequena, who appears in five episodes before "Remember Me Not" reveals she's a fairy who can implant Fake Memories, and an agent (or, as it turns out in the season finale, mind-controlled slave) of the Blind King. Dulcinea grows suspicious when she realises Toby's pictures don't include her, and we see her altering Puss's memories so that she was the first person he met in San Lorenzo, and Dulcinea's so that she'd been popping up all through the series insisting they were best friends. And when that doesn't work, she alters everyone's memories to believe Dulcinea is a monster from the Netherworld...
- The Amazing World of Gumball introduces a few new characters this way in the season 4 episode The Others. Since Gumball is so self-centered that he believes the entire world revolves around him, he (and thus, the audience) only ever saw the students of his own class. After opening his mind, he realises that there are dozens of students and several faculty members he never noticed before.
- In Ben 10: Alien Force, Kevin's father, Devin, was retroactively added in as a postmortem character from Grandpa Max's past. But Ben 10: Omniverse retconned this again by revealing Devin never existed and was a fake memory implanted in Max's mind during the year before Alien Force occurred.
- This was going to be one of the main points of the failed Buffy the Vampire Slayer animated spinoff. The show would retell the Scooby Gang's high-school years, with the addition of Dawn Summers, who was intentionally retconned into the fifth season of the show as a plot point, but had not appeared prior to that. Unfortunately, the show was never made.
- In Rick and Morty, the episode "Total Rickall" has the family become infested by alien parasites that breeds via fake memories and take the form of wacky characters. This starts off with parodies of typical sitcom characters such as Uncle Steve and Cousin Nicky and eventually spirals into the house being filled with all sorts of fantastical characters. Most prominent is Mr. Poopybutthole, who is not only there from the start, but is also edited into the intro. Eventually they realize that the parasites can only create happy memories and that the real ones are the people they have horrible memories of. However, Mr. Poopybutthole turns out to be real; he really is just that great of a guy.
- South Park: Parodied in "Red Man's Greed," when a random kid with "ALEX" written on his shirt appears in multiple scenes, each time giving a generic line any other character could have said. It takes until the very end of the episode for anyone to comment on it: