History CharacterDerailment / AnimeAndManga

** In the final season, this happens to Sherry. Ever since Sherry was a child, she has despised Iliaster and been determined to take revenge against them for the [[YouKilledMyFather death of her parents]]. After she disappears into the wormhole, it is later revealed that she has joined Z-One and by extension Iliaster and becomes an obstacle in the Signers' path from reaching Z-One. The reason for the abrupt change given is that Sherry has succumbed to a false hope of Z-One changing the past to give her a lasting bond with her parents again.

** Ash's Pikachu started as bratty and self-centered but over time received CharacterDevelopment to become a natural leader, who acted as a mediator to other Pokémon and had full loyalty to Ash. A common plot of Pikachu shorts (and the occasional filler episode) would be Pikachu being left in charge while the humans were away and [[OnlySaneMan struggling to control the chaos caused by the other Pokémon]]. Come ''Sun & Moon'' and Pikachu began regressing to how he was in Kanto becoming more selfish, rebellious, and mischievous, often ignoring Ash's orders and even attacking him for fun. If anything Pikachu became the most mischief-prone of Ash's Alola team and acted more like a child than a leader. This regression initially progressed to ''Journeys'' and became even worse. In episode 30 Pikachu was willing to run away from Ash all because he was spending time with Riolu. Riolu is a newly hatched Pokémon, which naturally requires extra attention. Pikachu understood this with Phanpy, Larvitar, Scraggy, and Noibat and [[BigBrotherInstinct even acted like an older brother to them]]. Yet, suddenly, Pikachu believes Ash no longer loves him. To add salt to the wound when Ash apologizes Pikachu accepts the apology... only after electrocuting Ash. Thankfully, by the second half of ''Journeys,'' Pikachu was more or less back to his pre-Alola self.

** Ash's Pikachu started as bratty and self-centered but over time received CharacterDevelopment to become a natural leader, who acted as a mediator to other Pokémon and had full loyalty to Ash. A common plot of Pikachu shorts (and the occasional filler episode) would be Pikachu being left in charge while the humans were away and [[OnlySaneMan struggling to control the chaos caused by the other Pokémon]]. Come ''Sun & Moon'' and Pikachu began regressing to how he was in Kanto becoming more selfish, rebellious, and mischievous, often ignoring Ash's orders and even attacking him for fun. If anything Pikachu became the most mischief-prone of Ash's Alola team and acted more like a child than a leader. This regression initially progressed to ''Journeys'' and became even worse. In episode 30 Pikachu was willing to run away from Ash all because he was spending time with Riolu. Riolu is a newly hatched Pokémon, which naturally requires extra attention. Pikachu understood this with Phanpy, Larvitar, Scraggy, and Noibat and [[BigBrotherInstinct even acted like an older brother to them]]. Yet, suddenly, Pikachu believes Ash no longer loves him. To add salt to the wound when Ash apologizes Pikachu accepts the apology... only after electrocuting Ash. Thankfully, by the second half of ''Journeys,'' Pikachu was more or less back to his pre-Alola self.

** Ash's Pikachu started as bratty and self-centered but over time received CharacterDevelopment to become a natural leader, who acted as a mediator to other Pokémon and had full loyalty to Ash. A common plot of Pikachu shorts (and the occasional filler episode) would be Pikachu being left in charge while the humans were away and [[OnlySaneMan struggling to control the chaos caused by the other Pokémon]]. Come ''Sun & Moon'' and Pikachu began regressing to how he was in Kanto becoming more selfish, rebellious, and mischievous, often ignoring Ash's orders and even attacking him for fun. If anything Pikachu became the most mischief-prone of Ash's Alola team and acted more like a child than a leader. This regression initially progressed to ''Journeys'' and became even worse. In episode 30 Pikachu was willing to run away from Ash all because he was spending time with Riolu. A Pokémon is a baby which naturally requires extra attention. Pikachu understood this with Phanpy, Larvitar, Scraggy, and Noibat and [[BigBrotherInstinct even acted like an older brother to them]]. Yet, suddenly, Pikachu believes Ash no longer loves him. To add salt to the wound when Ash apologizes Pikachu accepts the apology... only after electrocuting Ash. Thankfully, by the last third of ''Journeys,'' Pikachu was more or less back to his pre-Alola self.

* ''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. Sure, Uryu in the second meeting wasn't in a position to ''do anything'' about his hatred of Mayuri, being too badly injured to even stand up, but if anything that should make him him even ''angrier''.
** 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.

* The [=DigiDestined=] in ''Anime/DigimonAdventureTri'' act less like their original ''Anime/DigimonAdventure'' and ''Anime/DigimonAdventure02'' counterparts but more like angsty, selfish pricks who only go out to solve a problem if it affects themselves. For example, when Mimi goes to stop a rampaging Ogremon and accidentally screwed up by shooting down a media helicopter, she wasn't motivated by stopping the Digimon, but rather trying to make Digimon look good in front of humans. They also go out of their way to save Meicoomon, Meiko's partner just because she's a partner and blithely shoot down anyone who dares suggest the contrary, even when Meiko herself was the one who suggested it. It's also made clear that Meicoomon was too dangerous to keep alive and had to be killed in order to prevent further harm, and the [=DigiDestined=] shouldn't have any issues {{Mercy Kill}}ing out-of control partner Digimon anyways. ''Anime/DigimonAdventureLastEvolutionKizuna'' fixed the characterization issues, and Tai, Matt and Izzy are back to being closer to their original characterization, although they had still somewhat mellowed out compared to their child selves because of their age.

* The [=DigiDestined=] in ''Anime/DigimonAdventureTri'' act less like their original ''Anime/DigimonAdventure'' and ''Anime/DigimonAdventure02'' counterparts but more like angsty, selfish pricks who only go out to solve a problem if it affects themselves. For example, when Mimi goes to stop a rampaging Ogremon and accidentally screwed up by shooting down a media helicopter, she wasn't motivated by stopping the Digimon, but rather trying to make Digimon look good in front of humans. They also go out of their way to save Meicoomon, Meiko's partner just because she's a partner and blithely shoot down anyone who dares suggest the contrary, even when Meiko herself was the one who suggested it, despite that thing was obviously too dangerous to keep alive and had to be killed in order to prevent further harm, and the [=DigiDestined=] shouldn't have any issues {{Mercy Kill}}ing out-of control partner Digimon beforehand. ''Anime/DigimonAdventureLastEvolutionKizuna'' fixed the characterization issues, and Tai, Matt and Izzy are back to being closer to their original characterization, although they had still somewhat mellowed out compared to their child selves because of their age.

* ''Anime/NadiaTheSecretOfBlueWater'': The infamous island/Africa arc 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]].)

** Cassidy and Butch while initially popular characters being serious foils to Jessie and James fell into this after a severe case of VillainDecay and {{Flanderization}} in ''Anime/PokemonChronicles''. In this series of side stories, the two strong schemers became copies of Jessie and James without any of the HiddenDepths that made those two popular, to begin with. [[FullEpisodeFlashback "Training Daze"]] in particular hurt their image as it retroactively made it so they were '''always''' as incompetent as Jessie and James, which was the exact opposite of their original intent. This derailment would carry over to the main series, and its poor reception might be why the duo made no appearances from Gens V-VII. When the duo finally returned in ''Anime/PokemonJourneys'', it was revealed that they had quit Team Rocket and begun an honest living. Some saw this as CharacterRerailment for the duo having regained their competence, while others saw it as further derailment given prior series portrayed them as [[CardCarryingVillain reveling in being thieves.]]

* ''LightNovel/BakaAndTestSummonTheBeasts'' 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 reduced to that half the time. Thankfully, the last episodes seems to bring her back to rails.

* ''LightNovel/TheFamiliarOfZero'': Siesta 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/MayoChiki'': Kanade and Usami are both getting hit by this. 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.

* ''LightNovel/{{Tytania}}'': This 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.]]