* Priss Asagiri falls victim to this in the final episodes of ''Anime/BubblegumCrisis Tokyo 2040.'' She reveals to her love interest, ADP Officer Leon [=McNichol=], that the real reason she hated the AD Police was that they broke her favorite CD during a boomer attack. Before then, she was developed as a complex, mysterious, stoic loner. This revelation derails her integrity for the sake of cheap laughs and misguided social commentary.
* ''Manga/DotHackLegendOfTheTwilight'' did this with Silver Knight, who acted more like Crim rather than TheStoic he's known to be.
%%** The manga does this to Balmung, of all people.
* The infamous island/Africa arc in ''NadiaTheSecretOfBlueWater'' is notorious for distorting the characters' personalities and relationships with each other. Nadia herself suffers from this the most. While she is a troubled character in the central plot of the story, the filler arc changes her personality from a NotGoodWithPeople sort of character to a [[JerkAss totally unlikable, selfish, psychotic, cartoonish buffoon]]. It is hard not to watch any of these episodes without noticing how many times the writers press "reset" on the characters' personalities and relationships with each other. (The Lincoln Island and Africa arcs are especially insulting, for [[AssPull sidestories that feel very out of place with the main story arc, not to mention poorly thought out]].)
* Daichi Misawa of ''Anime/YuGiOhGX'', whose TeenGenius personality became grotesquely twisted out of shape until he began acting directly contrary to what had previously been shown. (Then again, a drastic personality change is {{justified| Trope}} if he really was [[EpilepticTrees raped by a love-crazed Amazon]].) He eventually snaps/has an epiphany and runs naked through the school grounds a la Archimedes, and then gets PutOnABus. He eventually returns but does little before deciding to live in another dimension with said love-crazed Amazon. This was arguably a minor attempt to return his character to its roots as he made this decision partly because he felt more appreciated in the other dimension than he did in his native one and acceptance/recognition was what he had sought from the start.
** Asuka Tenjoin goes from ActionGirl to FauxActionGirl to DamselInDistress.
* ''Anime/YuGiOh5Ds'': For quite a few people, the change in Aki's character was too abrupt, most of it within the space of one or two episodes rather than being more evenly spread out. To clarify: The only thing the [[DarkMagicalGirl former Aki]] and the [[SmittenTeenageGirl recent Aki]] have in common are their [[MsFanservice physical attributes]].
** This happens to almost everyone in the second season. For example, [[TheRival Jack]] [[IgnoredEpiphany forgets everything he learned in the Dark Signer arc]] and goes back to being a self-centered jerk, [[ActionGirl Aki's]] {{Chickification}} is taken even further to the point she becomes a FauxActionGirl, [[TookALevelInBadass Carly]] is demoted from Jack's LoveInterest to a comic-relief character with little more importance than the rest of his fangirls, etc.
* In ''Franchise/TransformersGeneration1'', Cyclonus and Scourge were a pair of dangerous, cunning, devious warriors. In ''TransformersHeadmasters'', they suddenly became a pair of bumbling idiots who kept getting in Sixshot's way, and wondered why Soundblaster lost all respect for them. They were quietly dropped from the show soon after.
** Rodimus Prime after the movie also suffered derailment, turning from 'plucky youth' into 'useless jerk' over the third and fourth seasons. It's like [[TheyWastedAPerfectlyGoodPlot they completely screwed up]] the chance to show a less invulnerable, more three-dimensional Prime.
* Nina Wang got hit with this ''hard'' after [[WhamEpisode Episode 16]] of ''{{Mai-Otome}}''. Before, she was a somewhat friendly [[TheRival rival]] to Arika and a more-than-competent fighter on track to become one of the greatest Otome ever. Afterward, she [[spoiler:underwent a FaceHeelTurn and killed tens of thousands of people to prove her loyalty to/love for her "father"]], and her rivalry was thrown on the back burner for all but one or two episodes during that period, and her position was snapped up by Tomoe for [[UnknownRival reasons unknown to Arika]].
* This occurred in ''LightNovel/{{Tytania}}'', and it happened to, of all people, Estrades- the man turns from a calm, devious schemer who was perfectly fine being ordered about by his brother Ajman to a wild, rabid, hateful person who despised his sibling with every fiber of his being. To top it off, his derailment is combined with a severe case of a mixture of the IdiotBall and TooDumbToLive when [[spoiler: he offs himself by shooting himself after tumbling down a flight of stairs.]]
* Dumas from ''{{Kiba}}'' starts off as the strong, quiet champion of Tempura/Templer, then [[spoiler: makes a shocking {{Face Heel Turn}} and would have lead Jimoto's invaders to overtake Tempura had not Zed's Spirit gone on a rampage and stopped them.]] The really interesting part was that Duma's reasons for this were pretty reasonable: because of his family history, he basically wanted to shape his own destiny. However, after those events, [[spoiler: he became a regular psychotic baddie whose sole purpose in life was betraying Tempura in ever way possible and becoming royalty.]]
* Brock from ''{{Anime/Pokemon}}'' was the voice of reason with occasional attractions towards girls in Kanto. When he got back from his [[PutOnABus bus trip]] during the Orange Islands FillerArc, he became a super freak with raging hard-ons every time he sees things with two legs and a vagina. [[spoiler:The writers caught on by the end of the Sinnoh arc and gave him a [[PutOnABus mercy bus ride.]]]]
** And his voice of reason status has apparently been reduced to just explaining to his comrades (and the audience) ''[[CombatCommentator every single move]]'' that gets made during a battle.
** Considering that Ash has battled various opponents in the past with impressive feats, you'd think he'd be able to beat Paul or Trip once without getting his ass handed to him. No matter what, post-Sinnoh Ash seems to fight like an inept beginner, especially considering his impressive victories in the past; and don't get anyone started on the ass whipping he gave to Fantina in a rematch.
** It was explained a few appearances in that Paul is pretty much just as experienced as Ash is. And while that is admittedly an AssPull, there is still no question he is smarter and a better tactician in the heat of the moment compared to Ash. Trip on the other hand, there is no excuse whatsoever that Ash should lose, or even have trouble with a beginner trainer, at all.
*** He eventually beats Paul in the Sinnoh League with the very same Infernape that Paul abandoned as a Chimchar. Although that brings up the whole point of how Paul [[KarmaHoudini never got any comeuppance for what he did in the past...]]
*** On that note, Paul's transition from JerkAss to a more considerate and caring trainer at the League tournament was way too abrupt and made little sense, with little to no explanation to it other than being used to finally put an end to his rivalry with Ash.
** In mid-Sinnoh, Ambipom was literally PutOnABus, for incredibly contrived reasons that made no sense given the Pokemon's previously established character. From the beginning Aipom/Ambipom was shown to love Contests, which eventually led to it getting traded to Dawn, the Contest Coordinator of the group. DP 124 has the characters participating in [[MundaneUtility Pokemon Ping Pong]], and Ambipom suddenly decides to leave her trainer and the Contests she loved so much to go off with a complete stranger and train for an activity she didn't even know existed before the previous episode. Many fans are not happy.
** The first example would be Ash's Charmander, which upon evolution into Charmeleon, went from similarly nice compared to Ash's other Kanto starters to volatile and uncontrollable. Upon evolution into Charizard a while later, it went even further to a borderline jerk that actually seemed to dislike Ash. Charizard's attitude even cost Ash his match ''at his first Pokemon tournament''. It was probably supposed to be similar to Pokemon above a certain level refusing to obey their trainers without a certain badge in the games, but it firstly still came off as odd, and secondly didn't stop until after Ash had gotten all eight badges, competed in the Kanto League, and gotten halfway through the Orange Islands arc... And even then only because Ash spent a lot of time in effort to keep it alive.
** Made worse in that the show can't seem to decide whether or not evolving changes who you are (Charmander's personality changes, Pikachu and Bulbasaur directly refuse to evolve) or if it changes your form but nothing else (most other evolutions including a Magikarp that retained its sweet personality for the Joy that looked after it).
* What in God's name happened to Graham Aker in Season 2 of ''[[Anime/MobileSuitGundam00 Gundam 00]]''? In Season 1 he was an obsessive Flag pilot, and totally loyal to [[{{Eagleland}} The Union]]. Then in Season 2 he's... an obsessed Japanese {{Otaku}} calling himself Mr. Bushido? Who acts like he just walked out of a Super Robot show? What. The. Hell. And the fanbase that decries the situation in Seed/Seed Destiny says nothing about it? Yes Graham's transformation ''is'' funny. The first time Mr. Bushido appears it's hard not to laugh at how hysterical he's become ([[TropesAreNotBad Tropes]]--even this one--[[TropesAreNotBad Are Not Bad]] after all). But it's still CharacterDerailment.
** He's [[CharacterRerailment rerailed]] in the movie... but [[RedemptionEqualsDeath at the cost of his life.]]
*** His derailment does have a partial explanation. He shows small hints of his otaku ways all throughout Season 1, but he's otherwise normal. In Season 2, whenever he's not fighting he does have moments where he does act normal, even telling Billy the "Mr. Bushido" moniker was not one he was purposely angling for, and when he meets up with Setsuna it's flatly obvious the man has been severely depressed for awhile and he reveals he immersed himself in his Japanese otaku ways as something of an escape from the pain. Unfortunately, the derailment arguement still holds water because the show does a poor job of explaining the whys and when of his plunge into OccidentalOtaku.
*** [[CuteAndPsycho Nena Trinity]] got derailed during the 2nd season, as well. After beginning to [[EvenEvilHasStandards develop standards]] and generally become less psychotic, a lengthy timeskip occurs and Nena is suddenly right back to her previously evil, batshit insane self with no explanation whatsoever given. [[DroppedABridgeOnHim And then she dies.]]
* [[Anime/MobileSuitGundamAGE Gundam AGE]] gives us Zeheart Galette. For most of the show he's a WorthyOpponent who makes a point of remembering his fallen comrades and subordinates and fights for every Vagan to return to the "Eden" that is Earth. After [[spoiler:Ezelcant reveals his true, SocialDarwinist agenda--the one that had him killing his own citizens--Zeheart devotes himself to it after about thirty seconds of hesitation. By the end, he's willing to throw away the lives of his most loyal aides for the sake of a diversion and wipe out multiple {{Mook}}s into the bargain. Perhaps it's the failure to reconcile these two wildly different characterizations that leads to his subsequent VillainousBreakdown.]]
* Kaede Fuyou from the anime ''{{Shuffle}}'' Is best known for going {{Yandere}} when the male lead chose another girl over her. If you described this to someone who had only read the VisualNovel that the series is based on, they would be ''very'' confused, since her behavior during the exact same situation in the game was [[TearJerker about as far from 'Yandere']] [[IWantMyBelovedToBeHappy as it is possible to get]].
* A case can be made for more than a few of the characters of ''CodeGeass'', but none more so than [[TheEveryman Ohgi]], initially the voice of reason of the rank-and-file Black Knights who understood the burden of leadership that rested upon Zero, he [[LoveMakesYouDumb lost the plot once he fell for Villetta]] and made many questionable decisions, with ultimately disastrous results.
* Siesta from ''LightNovel/ZeroNoTsukaima'' is a gentle and sweet {{meido}} in the first season, but in the next two she borders on BeAWhoreToGetYourMan, with no logic or explanation.
* [[LightNovel/ACertainMagicalIndex Kuroko]] [[Manga/ACertainScientificRailgun Shirai]] [[ZigZaggedTrope zig zags]] this. On regular plot (Both for ''Index'' and ''Railgun''), she's shown as a competent member of Judgement and a reasonable authority figure that just happens to have a crush on a girl, which is PlayedForLaughs but is hardly the only thing she does. On [[{{filler}} anime-only stories]], she suffers from full-blown CharacterExaggeration becomes a full-blown PsychoLesbian who's willing to resort to drugs to get Mikoto (which she thankfully fails at). And yet the second mode [[MisaimedFandom is much more popular]].
** Which is an example that TropesAreNotBad which while disturbing does make Kuroko a more interesting character if at cost of some of the show's morality, which is hardly that bad in light of the fact that show is [[ComedicSociopathy quite lacking in it in various areas anyway]].
* ''LightNovel/BakaToTestToShoukanjuu'' did this to poor Mizuki Himeji. In the first season she was a nice, sweet girl, with one scene hinting at {{yandere}}-ish HiddenDepths but mostly as an one-off gag and nothing serious. Come the OVA and second season, she's basically a clone of the the much-ruder Minami (Who herself suffered {{flanderization}} and became much worse than she was) only with longer hair and bigger breasts. Thankfully, the last episodes seems to bring her back to rails, while also smoothing over Minami a little.
* Kanade and Usami are both getting hit by this on ''MayoChiki''. Kanade is going from a sexually dominant, but playful and overall nice girl to a {{jerkass}} {{troll}} that has no problem on causing property damage and intimidating others with her BattleButler. Usami went from a nice {{tsundere}} to a generic angry tsundere, overlapping with CharacterExaggeration. Kanade eventually gets better, Usami.... is DemotedToExtra so nobody knows.
** However, both pale compared to UnluckyEverydude Kinjirou in the GeckoEnding. To summarize, the entire show is about him having gynophobia (fear of women) and the other girls trying to help him with that. Unlike some harem mains, he's not a pervert nor anything like that, and in fact the girls are worse than him. But in the GeckoEnding, he suddenly becomes a ''very generic'' pervert that nosebleeds when he sees Usami's panties and can't stop thinking of having sex with [[OfficialCouple Subaru]]. Which is the exact opposite of how he normally is. He also gets CharlesAtlasSuperpower out of freaking nowhere.
* Tails from ''SonicX''. In the first two seasons, while there was some heartwarming bonding between him and [[BadassGrandpa Chuck]], he was characterized as being someone extremely intelligent who happened to be a kid, rather than a kid who happened to be extremely intelligent as he is characterized in the games. He becomes derailed even more in the third season.
* In ''Anime/PuellaMagiMadokaMagica'', Kyosuke Kamijou (Sayaka's ChildhoodFriend love interest, who seems to think his relationship with her as strictly platonic) and Hitomi Shizuki (one of Sayaka's friends and TheRival for Kyosuke's heart) are probably [[TheScrappy the most hated characters in the series]] [[spoiler:(after Kyubey)]] for [[spoiler:sending Sayaka on her StartOfDarkness]]. However, their actions in the anime [[HumansAreFlawed are somewhat understandable]] and they do [[ThrowTheDogABone give Sayaka]] some [[HopeSpot Hope Spots]] (e.g. Hitomi tells Sayaka to face her feelings and gives her a day to confess to Kamijou). Additionally, both Hitomi and Kyosuke were unaware of all the problems that Sayaka had [[spoiler: such as Sayaka finding out that her soul got ripped out of her body and put into a SoulJar because no one tells Hitomi and Kyusuke anything. In the last few episodes, after Sayaka's death, it is revealed that Hitomi fell into depression and thinks [[ItsAllMyFault it's all her fault]] while Kamijou also seems to miss Sayaka.]] Unfortunately, these shades of gray are all dumped in the PSP game. [[spoiler:[[RonTheDeathEater Hitomi becomes a full-on]] [[AlphaBitch Alpha]] BitchInSheepsClothing, while Kamijou, Sayaka start decomposing due to her distance from her Soul Gem and calls her "a disgusting (understandable) ''monster'' (not so much)", then [[KickTheDog twists the knife further]] by adding "[[DarthWiki/WallBanger Shizuki is the only one I need]]!" ]] Ouch. However, the outcome of this game does depend on how you play it, so there are some scenarios where Hitomi and Kyosuke don't get character derailment. But, the derailment they get in some of the scenarios is still pretty bad.
* In Franchise/{{Naruto}}, [[spoiler:Obito]], at first a guy who strongly believed in ThePowerOfFriendship and could be the potential WhiteSheep of the [[spoiler:Uchiha]], becomes [[spoiler:Tobi]], a ruthless villain who wants to throw the world into despair and isn't afraid to threaten and harm newborns. All because [[spoiler:Rin]] died. [[HandWave Hand-waved]] in that the same Bloodline Limit that allows the Uchiha to unlock Sharingan also affects their brains, making them go crazy when someone they love dies.
* In ''Manga/{{Bleach}}'' Uryu seemingly has forgotten about how Mayuri tortured his grandfather to death. Instead of displaying open hatred for Mayuri when they meet up again, he only seems mildly annoyed with Mayuri, and his reaction is PlayedForLaughs. The show seems to be glossing over the first time they met and what Mayuri did to his grandfather and his entire clan.
** Yukio and Giriko from the Fullbring arc. They are each calm and quiet normally, but after receiving Ichigo's power, it went to their heads, causing them to become loud and boastful, Yukio declaring himself a [[AGodAmI god]]. Yukio, at least, seemed to return to normal after having the extra power taken away, so it may be a case of DrunkOnTheDarkSide.
** As WebVideo/YRulerOfTime points out, Orihime undergoes by this for the Hueco Mundo arc. She started the series having a lot of CharacterDevelopment, by learning how her powers work, being ThePollyanna in front of her bullies or enemies and being the optimistic BunnyEarsLawyer. Once the Arrancar Arc started, Orihime was demoted to LivingMacGuffin DamselInDistress, who could only wait to be rescued and cry for Ichigo to save her.
* In the ''Manga/KOn'' [[TheMovie movie]], Azusa becomes quite upset about the idea that Yui might have romantic feelings for her. Quite a few fans thought this was odd; Azusa might get exasperated by Yui's antics at times in the manga, but it was clear she wasn't against Yui's affection for her ''in principle'', and in the end even got very lose to confessing her feelings to Yui ''herself''.
* [[Anime/MobileSuitZetaGundam Zeta Gundam's]] Reccoa. She went from being a fairly capable, trusted member of AEUG with generally straight morals to [[spoiler: a TITANS officer]] who [[spoiler: willingly ''gassed'' an entire colony]]. Admittedly she tried to [[spoiler: delay it in the hopes that the AEUG would stop it]] but she [[spoiler: never attempted to stop it herself]]. This after she [[spoiler: used the evidence of the TITANS gassing a colony]] to convince [[spoiler: Emma to switch sides]] at the start of the series. It's idiotic enough that fans [[{{Fanon}} prefer to believe]] that [[spoiler: Paptimus has some kind of hypnotic NewType powers that he used on her]].
* Similar to the Fire Princess Ursa of ''WesternAnimation/AvatarTheLastAirbender'' example in the next page, we have ''Anime/TenchiMuyo'''s Mrs. Masaki. From Tenchi's point of view, his mother was this kindhearted woman and it was incredibly possible that Ryoko knew this, too. This characterization would carry over into ''Anime/TenchiUniverse'' and brief moments of ''Anime/TenchiInTokyo'' under her "Achika" name. Flash forward about six-seven years with the new OVAs and we find out that [[spoiler:Tenchi's mother, Kiyone, wasn't a kindhearted woman, but a total prankster who even treated her ''death'' as a joke and that the true kindhearted woman was Noboyuki's secretary Rea.]] Not only were fans pissed off, but so was Tenchi.