History HeWhoFightsMonsters / AnimeAndManga

* In ''Manga/BlueExorcist'' Mephisto Johan Faust (with the german theme of him) actually does the whole quote and dedicates it to the exorcists fighting in the Kyoto saga. He adresses first to his brother Rin himself who has to resist the pulsion of his blue flames lest he might burn all of his friends but actually most of the protagonists qualify. Especially Yukio whose all character arc epitomizes this trope.

* In one of the early cases of ''Manga/DetectiveConan'', the main characters visit a museum, where (of course) a murder happened to have taken place shortly before. Before the corpse is found, the characters discuss a certain painting showing a knight covered in blood from a demon he had just slain. After the case is solved, the curator gives another interpretation of the painting: That, due to being covered in the demon blood, the righteous knight himself becomes a demon. This is also used as a parallel to the case, as the murderer, who considered the victim a sort of "monster", ended up becoming a monster himself.

* ''Manga/DeathNote'':
** Light Yagami begins using the supernatural notebook to rid society of criminals, but soon his black list expands to include anyone who stands in his way for any reason, starting with the FBI, and he even intends to eliminate other "useless" people who aren't outright heinous criminals through accidents and disease. Along the way, he coolly manipulates the feelings of both people and shinigami. Repeatedly stating that he plans to become the god of the new world he is trying to create doesn't help matters, either. Ryuk even lampshades this, wondering aloud if Light will ultimately be the only bad person left, but he's just in for the spectacle.

* ''LightNovel/GoblinSlayer'' discusses this trope; the titular Goblin Slayer is deeply traumatized by seeing his hometown invaded by goblins, who tortured, raped, and murder the whole village while he could only hide and watch in terror. He subsequently devoted his entire life to hunting and killing goblins, obsessing over finding the most efficient ways to defeat them, studying their methods and biology, and doing little else. As a result, he's stunted psychologically and unable to form real relationships with other people, and comes off as [[HorrifyingHero rather disturbing]] to everyone else, particularly when he uses brutal but extremely efficient methods to kill goblins. Then he goes into their homes and kills them, all of them, leaving no survivors. In his own words, "to the goblins, I am the goblin." The trope is ultimately subverted; however much he enjoys killing goblins, he never loses sight of the fact that he would feel ''even better'' if there were no goblins at all in the world. He also has something that no [[AlwaysChaoticEvil goblin]] does- the ability to [[CharacterDevelopment change]].

** Sasuke now seems to have [[spoiler:realized that he was [[HeelFaceTurn manipulated]] by [[BigBad Obito]] after he listened to the First Hokage's story about Madara and his dreams for the village. To make matters worse, this is complete with Karin being [[LoveMakesYouCrazy Ok]] with the fact he tried to kill her immediately afterwards.]]
*** Not that it really made a difference. [[spoiler:He's instead turns into a psychotic revolutionary who wants to kill the Kages, Naruto and the Tailed Beasts and create a new world order. So Naruto has to fight him one last time. But when Sasuke finally hears from Naruto's own mouth that he still believes Sasuke is worth saving, he steps away from the brink long enough to dare Naruto: if you want to save me, ''BringIt''!]]

** Later in the story, Eren realises he's NotSoDifferent from [[spoiler:Reiner, Bertolt and Annie]], going so far to telling [[spoiler:Reiner]] that they/their ideals are the same, and they're carrying out their plans/attacks for the same reasons. He doesn't entirely seem to mind, however, so long as he achieves his goal of wiping out the enemy ([[spoiler:and no, it's not titans anymore, ''as such'']]), and he's accepted that that's his role in life.

** Teru Mikami uses the notebook to eliminate minor and reformed criminals.

* Seishu Akoya of ''Manga/KenganAshura'' is a police officer and a martial arts master who dedicated his life to "justice" and became a vigilante who slaughtered criminals with his bare hands. Over time he slowly became a psychotic KnightTemplar and extended his brand of "justice" to his victims' families and any rival fighters unlucky enough to get in his way. He beats his MoralityChain Hiyama for not giving him the results he wants as his MissionControl, and Adam Dudley accuses him of having "Film/DirtyHarry Syndrome".

* Ken, the pilot of Blade Gainer in ''Anime/ShinkonGattaiGodannar'', is one of these. His obsession with killing the Mimetic Beast that killed his wife causes him to mercilessly hunt every Mimetic Beast down, without regard to how much property damage or civilian casualties he causes. [[spoiler:His last words before his death is for Lou to not become someone like him. Lou continues to fight off every single Mimetic Beast alone, but Ken's words prevent her from going down his brutal way.]]

* This trope is given a bit of a workout in ''Anime/{{Monster}}'': [[spoiler:Johan's antagonizing of Tenma and Nina is, in many ways, because he wants them to chase him and make this trope come into effect. In some ways, he actually succeeded with Nina, who shot him during the events of the first episode; however, he utterly fails to break Tenma.]]

* ''Manga/FairyTail''

* In ''Manga/MahouSenseiNegima'':
** Haruna identifies [[spoiler:Kurt Godel]] as being [[http://www.mangafox.com/manga/mahou_sensei_negima/v30/c270/15.html one of these]]. He ''was'' an undeniable good guy as a kid, only to grow up into a completely manipulative {{jerkass}} little better than his enemy.

* ''Manga/MutekiKanbanMusume'': When Megumi accuses Miki (a prototype of TheBully seen on fiction, incredible strong and dumb) of bullying her, Megumi is truly surprised when Miki retorts that Megumi is the true bully – by using MaliciousSlander, sabotaging Miki’s work and setting tramps against Miki – a realistic depiction of TheBully in RealLife.

* In the Meakashi chapter [[spoiler:and by extension the Watanagashi chapter]] of ''VisualNovel/HigurashiWhenTheyCry'', [[spoiler:Shion Sonozaki becomes convinced that her family kidnapped and/or murdered her LoveInterest, Satoshi Honjou,]] and starts on a chain of murders of her own to avenge him, culminating in [[spoiler:murdering his little sister when his very last request had been for Shion to protect her. This leads to a HeelRealization and IgnoredEpiphany.]]

* ''LightNovel/GoblinSlayer'' discusses this trope; the titular Goblin Slayer is deeply traumatized by seeing his hometown invaded by goblins, who tortured, raped, and murder the whole village while he could only hide and watch in terror. He subsequently devoted his entire life to hunting and killing goblins, obsessing over finding the most efficient ways to defeat them, studying their methods and biology, and doing little else. As a result, he's stunted psychologically and unable to form real relationships with other people, and comes off as [[HorrifyingHero rather disturbing]] to everyone else, particularly when he uses brutal but extremely efficient methods to kill goblins. The trope is ultimately subverted; however much he enjoys killing goblins, he never loses sight of the fact that he would feel ''even better'' if there were no goblins at all in the world. He also has something that no [[AlwaysChaoticEvil goblin]] does- the ability to [[CharacterDevelopment change]].

*** Suzaku also qualifies in his quest of changing Britannia’s system, as in the beginning he attempted to be an InternalReformist against the racism and corruption within the government, but as things progress due to the above incident, he

* ''LightNovel/GoblinSlayer'' discusses this trope and explores it, with the titular Goblin Slayer being deeply traumatized by seeing his hometown and sister invaded by goblins, who torture, rape, and murder the whole village while he could only hide and watch in terror. He subsequently devoted his entire life to hunting and killing goblins, obsessing over finding the most efficient ways to defeat them, studying their methods and biology, and doing little else. As a result, he's stunted psychologically and unable to form real relationships with other people, and comes off as [[HorrifyingHero rather disturbing]] to everyone else, particularly when he uses brutal and cruel but extremely pragmatic and efficient methods to kill goblins.

** Strangely, Konoha itself. From how they treated Naruto in the beginning, it's pretty clear that they aren't the paragons of virtue. As a military government in a feudalistic world, they do pretty shady things to survive and keep peace, including [[spoiler:kill the Uchiha Clan after, at least according to [[UnreliableNarrator Obito]], blaming the Fox Invasion on them and outcasting them, prompting them to try a coup.]] Danzo, most of all, claims to want Peace by any means necessary, but his main goal is promoting Konoha's power across the world, with him on top, naturally. Danzo is also personally responsible for ''creating'' many of Konoha's greatest enemies, by ruining people's lives to the point of wanting revenge on Konoha in the name of the village's safety. [[spoiler:Itachi goes here as well, as he is willing to kill his family and go down in history as a murderer and psychopath just to keep the village safe AND protect Sasuke. Though this could be seen as a SadisticChoice given to him by Danzo.]]
** Hanzo of the Rain village is also implied to have fallen to this trope; in his youth, he was a WorthyOpponent of Mifune's who spared his life for fighting with honor and dreamed of uniting the ninja world; years later, he's a paranoid dictator whose endless warmongering has turned his country into a god-forsaken hellhole, and who crosses the MoralEventHorizon when he attacks Nagato and Yahiko's peaceful protest group out of fear that they'd try to usurp him. [[spoiler:This results in Yahiko and dozens of others dying horribly, Konan being scarred for life into an emotionless BrokenBird, and Nagato being crippled for life, going insane, and becoming the aforementioned Pain.]]
** Naruto himself almost fell into this trope; early Post-TimeSkip, his fury at the douchebaggery of Orochimaru and Akatsuki causes him to go [[SuperPoweredEvilSide Biju-mode]] more and more, each time faster as he continually calls upon the Ninetails. Kabuto even points out that Naruto wants to save Sasuke so much that he's willingly turning himself into a monster to do so. Luckily, Yamato sets Naruto straight and our hero becomes far less willing to transform until he can do so without losing his mind. [[spoiler:Until Pain seemingly kills [[LoveInterest Hinata]] in front of Naruto. In his rage Naruto takes his Biju-mode even further than ever before, transforming first into 6-tails and then 8-tails mode, and is on the verge of ''willingly freeing the 9-tails entirely just so it'll kill Pain for him'' when his fathers spirit intervenes to stop him.]]

** Sasuke now seems to have [[spoiler:realized that he was [[HeelFaceTurn manipulated]] by [[BigBad Obito]] after he listened to the [[AssPull First Hokage's story]] about Madara and his dreams for the village. To make matters worse, this is complete with Karin being [[LoveMakesYouCrazy Ok]] with the fact he tried to kill her immediately afterwards.]]

** Naruto himself almost fell into this trope; early Post-TimeSkip, his fury at the douchebaggery of Orochimaru and Akatsuki causes him to go [[SuperPoweredEvilSide Biju-mode]] more and more, each time faster as he continually calls upon the Ninetails. Kabuto even points out that Naruto wants to save Sasuke so much that he's willingly turning himself into a monster to do so. Luckily, Yamato sets Naruto straight and our hero becomes far less willing to transform until he can do so without losing his mind.

* Kurapika from ''Manga/HunterXHunter'' seems to be turning into this - his clan, the Kura clan, was wiped out by the Phantom Troupe, and as such, he has dedicated himself to hunting them down (the sole exception being [[TheMole Hisoka]], who wasn't a member at the time), but his methods increasingly feel like they wouldn't be out of character if they were performed by one of the Troupe.

** It's been stated that those who use too much Dragon Slayer Magic take the risk of becoming a dragon themselves. [[spoiler:Acnologia was once a Slayer who wanted {{revenge}} on the dragons, but after transforming into one himself his list expanded to the point he wouldn't mind if he just [[OmnicidalManiac wiped out the rest of the world too in the process]]. Irene Belserion was a proponent of human/dragon relationships and made Dragon Slayer magic to fight the human-eating ones, but her own transformation and the fear and hatred her people treated her with (coupled with the trauma of realizing she could never again be human) turned her into a {{sociopath}}

* In ''Manga/FairyTail'', it's been stated that those who use too much dragon slayer magic take the risk of becoming a dragon themselves.
** [[spoiler: Devil Slayers like Gray aren't exempt from this either, as Invel said that Devil Slayers will eventually become the demons they fight. Gray himself almost becomes this when he tries to kill Natsu/E.N.D. .]]

** Seems to also be the case with both [[spoiler:Eren Kruger]] and [[spoiler:Zeke Yeager]], who each claim they're [[spoiler:trying to save the Eldian people]], but have only ever been shown [[spoiler:attacking and killing Eldians (and turning them into titans, the very thing they're trying to stop) -- with no apparent guilt]]. Granted, it's hard to know if they're telling the truth (especially in the case of [[spoiler:Zeke]]), but the idea seems to be that [[spoiler:to protect the ones you love you have to become a monster and throw away your humanity in order to succeed, perhaps so that you ''don't'' feel any amount of guilt to hold you back]]. [[spoiler:Kruger]] brought up that love is important in fighting your enemy, and that you mustn't forget it, which could be referencing this trope, but it hasn't been clarified yet]].