Elfen Lied: During Lucy's childhood, she made friends with another girl who promised to keep the fact that Lucy was taking care of a puppy a secret from a group of boys who frequently bullied her. Eventually, the boys found out about the puppy and beat it to death in front of Lucy while making her watch. It turns out the girl Lucy made friends with had deliberately told the boys about the puppy, and while she's pretending to cry about it and feel bad about what she did, we see her smile through her crocodile-tears. Lucy then snaps forever and killsher along with the bullies.
Tower of God has several people like this: Ho, Nia, and most notably Rachel. Later, Apple, Koon's hacker in the second season, turns out to be a FUG agent.
Sae to Momo in Peach Girl for the first couple of volumes before the two genuinely become friends.
And Sae gets a taste of her own medicine when she falls for Ryo, who's just as manipulative as her. The betrayal part comes into play when he sets Sae up to do a porn video without her knowledge. Thankfully, Momo saves her.
Gankutsuou: In the beginning The Count seems to like Albert when in reality he only views him as a tool for his revenge. However, as time goes on, he finds himself developing real feelings for Albert which cause him lots of angst and heartbreak, but ultimately save him in the end.
Also, Peppo to Albert. Though she/he (?) eventually develops actual feelings for him.
In Naruto Kabuto usually presents himself as this harmless, bumbling oaf with Nerd Glasses, but is in fact the subordinate of the Big Bad Orochimaru, and Naruto seems clearly angry and upset when he realizes this because he had originally believed Kabuto was on their side since he helped them by giving them information and the like.
Shiranami to Hotaru in the Six-Tailed Beast arc.
Also, Yashamaru, Gaara's uncle. At first, Gaara thought that he was the only one that cared about him. Yashamaru taught Gaara about physical pain, emotional pain and love; concepts Gaara was completely unaware of in his childhood. He was commanded by the Fourth Kazekage to assassinate Gaara, but was given the choice in deciding whether he wanted to proceed or not. Yashamaru willingly accepted the command in order to avenge his older sister's premature death. The assassination attempt, however, ended in a desperate suicide mission and ultimately failed. Before he died, he told Gaara that no one had ever really loved him, not even him. This left Gaara even more of an emotional wreck than he already was. His suicide bombing attempt on Gaara's life caused Gaara to become psychotic. Yashamaru's last words, to Gaara, were "This is it. Please die." It's revealed much later that he truly did it under the orders of the Fourth Kazekage (Gaara's dad) as part of a Secret Test of Character, and that he had objected to such a move but ultimately had no choice.
In the second Shippuden movie Shinnou turns out to be one for Amaru. Amaru is quite shocked, but separates the person who taught her medicine and served as an inspiration to save lives and the person who is the Big Bad.
Bleach: Aizen does this when stabbing Hinamori while hugging and praising her, as well as betraying everyone in Soul Society (who adored him) after revealing the fact that he has always been against them.
The first time you properly see Izaya Orihara in the Durarara!! anime, he spends most of the episode having a suicidal and unstable girl named Rio, that he pretended to sympathize with and be friends with online, kidnapped and then orchestrating her rescue, only to hold poor Rio over the side of a building, toy with her desire (or lack thereof) to actually commit suicide, and then wander off to watch from a distance as Rio's despair reaches its peak and she decides to jump anyway. Luckily for her, Celty was a little more worried about her safety and saves her.
Hot Gimmick: Azusa does this to Hatsumi, making her fall in love with him before trying to have his friends gang rape her out of revenge.
Griffith of Berserk was never a nice guy, even before his Face-Heel Turn. A good example of this is how he treats Princess Charlotte, who's genuinely in love with him, as a Meal Ticket while still pretending to be in love with her.
The only person he was remotely honest with was Guts. He has a catastrophic breakdown when Guts leaves the Hawks due to wanting to stand on even ground with him and feeling that he was unable to as his subordinate.
Kyouko Mogami of Skip Beat! initially followed her childhood friend Shou to Tokyo to help him to get into a music career. Although Shou didn't help her at all and mistreated her, Kyouko still believed that all her efforts (doing several part-time jobs, paying for his training, being his de-facto unpaid maid) would be eventually repaid with love and gratitude. (Plus, Sho's parents were considering to make her the heiress of the family business instead of Sho.) Until she learns, from the mouth of Shou himself, that he has no feelings towards her, and the only reason he asked her to come with him was because he knew she would act as his personal maid for nothing. So she snaps, decides not to take it anymore, and makes the resolve to get revenge on him by trying to become as famous as him.
Otome's "friends" Natsumi, Minami and Kumi do this to her in School Days. Otome is betrayed by them twice: they first videotape her having sex with Makoto, the guy she likes, and show the tape to the whole school, and then they have sex with him behind her back. And they do this for no reason at all.
Uzuki to Yuki in Uragiri wa Boku no Namae wo Shitteiru. As he himself tells Yuki in episode 2 "You're a nuisance. I hate your goody two-shoes, know-it-all act. I'm not your friend. I felt bad for you, so I thought I'd try being nice, but you misunderstood. No one needs you." But its refreshingly subverted when its revealed Uzuki was just deeply hurting from being abandoned by his parents and lashed out at others. He and Yuki become friends again after Yuki gets rid of the demon that was possessing Uzuki and feeding on his negative emotions.
And in episode 12 Kanata, Yuki's best friend, does this when he reveals to Yuki that he is actually the Big Bad Reiga.
Code Geass: Rolo, Lelouch's fake little brother, was actually a teenage assassin charged with the task of keeping an eye on Lelouch in case he regained his old memories. When Lelouch found out, he continued treating Rolo kindly and orchestrated a situation where Lelouch could pretend to risk his life to save Rolo, winning his trust and bringing him over to his side. After Lelouch's real sister died or so we think, he admitted to Rolo that he was just using him, actually hated him, and had tried to kill him on several occasions. Nevertheless, without being asked or influenced by Lelouch's Geass, Rolo sacrificed himself to protect Lelouch, since he believed that even when Lelouch lied to him, his own love for Lelouch was sincere.
And Empress Marianne, Lelouch's mother, whom he looked up to and adored is revealed to actually be quite the Magnificent Bitch.
Akio of Revolutionary Girl Utena is The Casanova to the extreme and does this to a lot of people, most notably to Utena. Another example is when Nanami walks in on her beloved brother Touga making out with a member of her old gang, Keiko, and overhears him say he never loved her to begin with, and her ex-friend claims she has no connection to her anymore either.
Touga is actually very good at this, and his other victim aside of Nanami is Saionji. Yes, Saionji was a Jerk Ass, but not even he deserved Touga's horrible treatment.
In the yaoi manga Under Grand Hotel an inmate named Norman is in love with Swordfish, who is in love with Sen, but pretended to be in love/friends with Sen so he could get closer to Swordfish. He tried to persuade Swordfish to kill Sen but that didn't work. So, on one occasion when there was a scuffle going on he tried to get Sen out of the way by stabbing him with a pencil but accidentally ends up stabbing his inmate Walter instead who was trying to protect Sen in the hope of getting protection from Swordfish. When he finds this out, Norman holds a knife to Walter's neck telling him, "If you don't want to die, don't butt in again Walter!"
In Pandora Hearts, Jack Vessalius turns out to be this to Arthur Barma in the past and Oz in the present. It can be argued that he was also this to Oswald/Glen, though it's very possible the two were genuine friends before Lacie's death drove Jack insane.
Lancia of Katekyo Hitman Reborn! is a young Mafia boss who took Mukuro Rokudo in as a child. However he was betrayed and brainwashed by Mukuro's Hypnotic Eyes, which forced him to kill his entire family.
Kuro from One Piece does this to Kaya as part a lengthy scheme to gain her trust so he can claim her fortune and retire from piracy. When Kaya finds out his true nature, he freely admits that he hated having to act the kindly butler to her.
It is again used by the CP 9 as they act friendly, become well-loved members of Water 7, befriend many members of Dock 1, including Paulie, but when they reveal themselves, they also reveal that they never had any attachment to the city or to the people inside it. Paulie can't believe it at first, and asks his traitorous good friend Rob Lucci:
Paulie: ...I thought...!! I REALLY THOUGHT WE WERE FRIENDS!!!
When Riff from Count Cain has his confusing Face-Heel Turn and "dies," it is revealed that Riff, the manservant personality was never actually real. This is Cain's manservant by the way, the only one who can "see his scars, make his tea, and tie his shoelaces." Epic Tear Jerker.
Highschool of the Dead: The first chapter/episode has a pair of girls proclaiming their friendship while running hand-in-hand as they attempt to escape the zombies overunning their school. That is, until one gets caught unexpectedly and is promptly abandoned to die by her "friend", who kicks the other girl to force her to let go of her hand so she could save herself. But is immediately caught and killed, as well.
Sara to Yuuri in Kyo Kara Maoh. However, Sara does save Yuuri after betraying him and they become friends again, subverting the trope.
In the backstory of Special A, Akira's childhood friend Sayo only hung out with Akira because she was rich. Yahiro, a real friend to Akira, drove Sayo away to protect Akira but let Akira believe he did it because he was just being a jerk to spare her the truth. In the present she still hates him.
Hamatora In the new season, it has Art... Who used to be Nice's friend, but turned againt him and his friends..
This trope was conversed in Chapter 8 of Gekkan Shoujo Nozaki-kun, animated as the first half of Episode 4. Nozaki was initially unwilling to consult Tomoda when playing Mikoshiba's Dating Sim as he sees anyone who appears to be friendly to the protagonist in fiction to be this—after all, Nozaki is a Shoujo Genre author by trade. After a brief explanation of the trope itself by Nozaki, Mikoshiba complained Nozaki for being Wrong Genre Savvy.
In the final part of the Justice League arc Trinity War, the Atom (Rhonda Pineda) who was first thought to be a sleeper agent for the JLA working on the Justice League, but was revealed to have put a small piece of Kryptonite in Superman's brain, poisoning him. She revealed that she was a sleeper agent from Earth 3. before this, she was one actually quite friendly to everyone.
Films — Animation
Gothel in Tangled tried to make Rapunzel believe that Flynn was this, that he was only after the crown and never cared for her. She nearly succeeded, until Rapunzel remembered her true heritage and realized that Gothel had kidnapped her and Flynn was going to be executed.
In Frozen Prince Hans eventually reveals that he simply wanted to get close to Anna in order to marry into the royal family. After learning that Anna is dying and can only be saved by true love, he has this to say.
"Oh Anna... if only there was someone out there who loved you.”
The Truman Show. Truman's "best friend" since childhood (who is really an actor) at one point appears to truly be listening to Truman's plight and confusion, almost seeming to really want to help his buddy understand the crap that's going on with his life. However, he allows himself to be instrumental in the biggest Mind Screw the studio pulls on Truman in bringing his "father" back from the grave. He later leads the hunt to capture Truman once he starts escaping.
Though there is a good scene when he clearly struggles with the lines that the producer is feeding him through his ear piece. He visibly chokes a little when he's instructed to reaffirm his best friend status and that he would never lie to him.
Though that could be just good acting.
There are deleted scenes that indicate that Marlon/Louis does in fact feel guilty about what he's doing to Truman, and the (actual, real-life) actor said that the character has a drug addiction from the stress.
10 Things I Hate About You. Chastity, who is supposedly the best friend of the second leading lady, Bianca, not only goes out with her original date, Joey, but even rubs her face in it afterwards by revealing that Joey only took her out on a bet with his buddies in the first place.
1984: O'Brien tricks Winston and Julia into thinking he's their friend and gets him to trust them, especially as far as identifying himself as a member of the Inner Party but is really a member ofLa Résistance. He then organizes the raid to capture the protagonists, brings them to the Ministry of Love and oversees their torture and brainwashing.
In one of The Southern Vampire Mysteries novels, it's revealed that Bill was ordered by his queen to seduce Sookie, as part of a plan to use her telepathy for whatever it is a vampire queen needs a telepath for.
Herald Myste had this pulled on her as a child three times by guys using her to get close to her best friend (the most attractive girl in the neighborhood). Prince Karathanelan tricks Selenay into wedding him, but doesn't survive the "betrayal" part.
Wormtail does this when he betrayed Harry's parents to Voldemort, even though they were his best friends - though he was more of a Fair Weather Friend who sold out his buddies in order to save his own life. When his remaining friend Sirius, chased him down after James and Lily's deaths, Wormtail shouted that Sirius had been the one to sell out the Potters, caused an explosion that killed a dozen innocent people, and faked his death before escaping, pinning the murders of himself, the Potters, and all the other people on Sirius.
Tom Riddle is a more straight example, doing this to Ginny and, to a lesser extent, Professor Slughorn.
In The Traitor Game, Michael comes to believe that Francis has spent their friendship laughing about their games with his friends. The consequences are nothing short of disastrous.
The fox and the cat in The Adventures of Pinocchio, upon discovering Pinocchio has several gold pieces, proceed to mooch off of him, try to rob and hang him, and later swindle him, all while pretending to be his friends. Unlike the Disney version, however, they do get their comeuppance in the end, and when they beg for Pinocchio to help them, he shows no forgiveness.
Ser Dontos acts like a friend and confidant to Sansa and promises to help her escape the Lannisters to repay her for saving his life. In actuality he's working for Littlefinger and is willing to sell her out to whoever will pay him for it.
Shae to Tyrion, she acts like she cares about him but she's really just a Gold Digger who's more than happy to accuse him of crimes he didn't commit for the promise of riches and status.
One of the themes of Daenerys' storyline is the constant presence of these and her doubts to tell her real allies from those who seek to use her or will at some point betray her. The appendix section dedicated to her in A Dance with Dragons event lists "Her uncertain allies, false friends, and known enemies."
The first Night Huntress book has a classmate cozying up to Cat, only to try to kidnap her for a white slavery ring. Turned out she did this to a lot of girls.
In Oz Schillinger arranges for Chris Keller to meet Tobias Beecher, Schillinger's former sex slave, with the intent of gaining his trust and seducing him. A mutual attraction instantly forms between them, and the two eventually exchange confessions of love. Unfortunately for Beecher he finds out that the man he fell in love with was working with his arch enemy all along (and informs him that he never loved him right before breaking Beecher's arms and legs). Keller clearly enjoys the beating, but is briefly seen experiencing a moment of regret when he returns to his empty cell and eventually realizes that he has fallen in love with Beecher.
Morgana, with Uther and Arthur, since the beginning of Merlin season 3.
Columboadmits to doing this (once) at the end of one of the ABC TV movies.
Nina Myers on 24 is the show's biggest example of this, being Jack Bauer's primary confidant at CTU in season 1 until she killed his wife while trying to escape after being outed as a mole working for the bad guys. She would then go on to become a recurring villain in seasons 2 and 3.
In Robin Hood, Marian cultivates a "friendship" of sorts with Guy of Gisborne so that she can pass on information to Robin. She even goes so far as to pull off a perfectly executed Decoy Damsel ploy, which Guy falls for hook, line and sinker. Guy was something of a False Friend himself considering he seems more than ready to have Marian punished if she disobeys him, and when he learns that she's in love with Robin Hood, he stabs her to death.
HG from Warehouse 13 does this using the other agents to get an artifact so she could destroy the world though she does somewhat become the mask, getting talked down from doing this when her friend tells her to shoot her instead of being a coward and killing her with the rest of the world.
Myka: If I am wrong, then kill me. Do it! Kill me now! I mean, we're all gonna die anyway right, so what's the difference? So shoot me! Shoot me now. Kill me. But not like this. Not like a coward. I want you to look me in the eyes and. Take. My. Life.
In Game of Thrones, Ramsay Snow, aka "The Boy", pretends to be Theon Greyjoy's only friend and ally. He helps the latter escape his torture, kills several of their pursuers who are trying to gangrape him...only to lead him back to the torture chamber. Why did he do all of this? Because it was fun.
There's an odd version of this in the Phoenix Wright: Ace Attorney series. Dahlia Hawthorne tricks Phoenix into thinking she's in love with him, just so she can get a piece of evidence back that incriminates her for a previous murder. She tries to kill him when it doesn't work. It's subverted when Dahlia has her sister impersonate her for a while, and her sister actually does fall in love with Phoenix.
Kristoph Gavin became Phoenix's "friend" only to closely monitor his activities after Kristoph got him disbarred, and ends up framing him for a murder. Phoenix was aware of this, however.
A variation occurs in Specter's ending in Twisted Metal Black; the man of her dreams has been forced to marry her by way of some brain surgery, but he's still able to tell her "I... will... never ...love ...you."
The Boss in Metal Gear Solid 3, before defecting, was Snake's mentor and one of his closest friends. She celebrates her Face-Heel Turn by beating him up and stealing his rescued hostage.
Subverted and played straight, however, as The Boss was really a Fake Defector sent in by the U.S. government to play the False Friend to Big Bad Colonel Volgin.
In Uncharted 2, Harry Flynn did this to Nathan Drake at the end of the Museum mission, causing poor Drake to rot in prison for 3 months.
If you get his good ending, it turns into Becoming the Mask... maybe. If you believe anything he says by that point!
If you've ground White magic enough to have gotten the spell Empathy, you can use it on him when you next talk to him. He's telling the truth about how he feels now.
In Dragon Age II, it's possible for Hawke to do this to Fenris when he finally confronts his former master Danarius by handing Fenris back to him. This will devastate him so much that he'll simply submit without a fight. However, this act is considered a Moral Event Horizon by the other companions save for Anders, who hates Fenris.
Touhou: Mystic Square features the fire and ice magicians Yuki and Mai as a Dual Boss. If you defeat Mai first, Yuki will be furious and crank up the heat. But if you defeat Yuki first, Mai will smugly declare that her comrade was nothing more than "dead weight" dragging her down (though ironically Mai's regarded as the easier of the two). Mai's leitmotif is appropriately named "Treacherous Maiden ~ Judas Kiss."
Hatoful Boyfriend sequel Holiday Star makes it clear this was the case for Hitori Uzune and the original Nanaki Kazuaki, a quail whose clinical depression was exploited by Hitori to double-cross him in a suicide pact and steal his identity. The betrayal caused Nanaki's spirit to become an Eldritch Abomination hell-bent on eternal companionship.
Upon his introduction in Mega Man 7 Bass presented himself as a possible friend and ally to Mega Man. When he was hurt fighting Shade Man, Mega Man allowed him to go to Doctor Light to get repaired. Once all the Robot Masters are defeated he discovered that Bass betrayed him, wrecked the lab, stole his upgrades, and hurt Doctor Light. Wily then brags about how Bass was his creation to get closed to Mega Man and how he was going to use his own upgrades on Bass to destroy him. Needless to say, Mega Man was pissed and probably one of the reasons why he was willing to kill Wily at the end of the game.
Ellen to Viola in The Witch's House. Ellen tricked Viola into sympathizing with her by telling her about her illness and the way her parents neglected her. Ellen just wanted to be "friends" with Viola so that she could steal her body using evil demonic magic.
MegaTokyo. Miho did this to Piro some time before the start of the series.
In The Gamers Alliance, Ferron befriends Refan during the Great War but does so only for two reasons: to avenge his lover who died by Refan's hand and to use Refan to get rid of The Dragon who had also wronged him (hoping that the two weaken each other enough in battle so that he can finish both of them off).
In Worm, Taylor tries to become this to the supervillain gang the Undersiders, but finds herself Becoming the Mask.
Felix in the 12th season of Red vs. Blue. It turns out that he'd been working with Locus all along, and was hired to wipe out the entire population of Chorus.
In Hercules the Big Bad Hades is unable to defeat his enemy Hercules because he is unaware of his weakness. So he instructs Megara to get close to Hercules and they both end up falling in love. However, before she can tell Hercules the truth Hades ends up telling Hercules about how Meg was working for him all along in the most cruel manner possible.
She's much, much nastier in the comics, as Terra was not a lost girl brainwashed by Slade. She was a pure psychopath that Slade was almost scared of (You read that right). Worse is that she was also Slade's underage girlfriend. What makes it especially hilarious is that at no point in the lead-up of the comic arc does she ever really pretend that she doesn't dislike nearly everyone on the team nor isn't lying constantly to them, so the Titans, in retrospect, were Too Dumb to Live.
Malchior is this to Raven in the "Spellbound" episode.
And Blackfire, Starfire's sister, who pretended to care for her sister while framing her for the crimes she committed so Starfire would get taken to jail instead. Starfire eventually finds out the truth and engages her in battle which leads to Blackfire rightfully getting captured by the police.
Done to Bart Simpson by Jessica Lovejoy. She pretends to like and befriend him, only so she can act as bad as she wants, knowing that if she gets caught, she can always blame Bart and let him take the fall. If not for Lisa, it would have worked.
A Heel-Face Turn example occurs in Avatar The Last Airbender. In "The Boiling Rock", Azula gets this after Mai and Ty Lee turn their backs on her. It is possible that they were never friends with her in the first place, since they were scared of her. It's also possible that she just went too far this time and they weren't willing to put up with her any longer.
Brought up once in the original Thunder Cats. "Better an honest enemy than a false friend."