History Main / TheDarkSideWillMakeYouForget

* ''Manga/DeathNote'': While Light Yagami starts out killing criminals with the idea of it bringing about justice, he starts to slip once the authorities get on his case, as he begins to kill innocent people for merely getting in his way. It gets worse after the TimeSkip, where he has fully bought into the idea of [[AGodAmI being the God of his own new world]], and he is beginning to seriously entertain the idea of also expanding his definition of "undesirables" to people who are committing the "crime" of being unproductive to society.

** Sasuke is a poster child for this. While he was always firstly driven by his wish to take vengeance upon his brother for murdering their family, his time in Konoha made him connect to the members of his team. The lure of revenge was too great until he decided to break those ties. [[spoiler:[[MotiveDecay His motives have rapidly degenerated]] after joining with Tobi. Initially after learning of the truth behind his brother's murder of his clan, Sasuke simply wanted revenge against the Village Elders who manipulated him. Now he won't settle for anything less than the complete genocide of anyone who lives in Konoha. There's some hints that Sasuke is being influenced by something (Madara claims the Uchiha bloodline is TheDarkSide), probably an AuthorsSavingThrow given that during the summit arc, he rather suddenly turns into a cardboard villain after gaining Susanoo (amongst other things, he abandoned another set of teammates that he seemed to care about earlier, who in the previous arc had saved him from being killed)]].
** Orochimaru was revealed to be a victim of this. The horrors of war and realization of his own mortality gradually twisted his dream of living long enough to meet his reincarnated parents into a tangible goal of discovering immortality.

** Originally, Zamasu just wanted the gods to be more involved with mortal affairs so they would stop misusing the knowledge given to them by the gods. At worst, he wanted the gods to stop protecting mortals since [[HumansAreBastards they're not worth it]]. After he meets and fights Goku, however, he goes off the deep end and decides that mortals are foolish ''and'' dangerous and need to be destroyed for the peace of the universe. [[spoiler:To that end, he kills his own master, takes his Time Ring, uses the Super Dragon Balls to take Goku's body, and murders him and his family [[EvilIsPetty out of spite]]. By the time Zamasu (now Goku Black) reaches Earth, he's wiped out all the gods in the future timeline, is clearly insane, and sees himself as the one true god of TheMultiverse along with Future Zamasu.]] Whatever nobility he may have had in his goals is long gone.

** Toffee eventually shapes himself as the BigBad of the series. WordOfGod [[https://www.youtube.com/watch?v=bme4NT7FleE compares him]] to Magneto, as someone who is trying to do good in "the wrong way". This might explain his initial [[spoiler:revolt]], but by present time, he seems to be just a ManipulativeBastard with no end goal in mind.
** Eventually, this trope is downplayed. Toffee's goal of "good" is in [[spoiler: ridding the realm of magic as he views it as dangerous and something Star comes to agree with.]] On the other hand, later episodes show he was always a jerk (even back as an adolescent, being reminiscent of a punk gang leader) and that his complaints seem dishonest since his race, the Septarians, are invulnerable with a strong HealingFactor that only magic can harm. Even most other monsters were afraid of his kind, making his own goals of "good" seem hypocritical when considering his race's own talents and him being afraid of something that can actually hurt him.

** Asajj Ventress spent many of her early years training under a Jedi who treated her with respect and seemed like the happiest days of her life. Then her master gets killed, she goes on a RoaringRampageOfRevenge, Dooku recruits her, she is now his apprentice and she goes around killing Jedi in revenge for not being there for her master.

* ''WesternAnimation/TeenageMutantNinjaTurtles2012'': Shredder's love for Tang Shen, and her choosing Splinter over him, is [[LoveMakesYouEvil his primary reason for turning evil]]. By the time of "Requiem," he's fallen so far that he no longer seems to care about Tang Shen at all, having absolutely zero qualms against [[SpeakIllOfTheDead mocking Shen's death to Karai's face]] by declaring that it's fitting that Karai will [[KillItWithFire die in the same manner as her mother]].

* ''Literature/TheWheelOfTime'' has an odd example in protagonist Rand Al'Thor. After he [[spoiler:channels the True Power, which is derived directly from the Dark One]], he undergoes an [[JumpingOffTheSlipperySlope immediate personality change,]] becoming incredibly paranoid, very harsh toward anyone who he perceives as threatening or even disagreeing with him, and abandoning his previous [[WouldntHitAGirl refusal to kill or harm a woman]]. However, the extraordinarily stressful circumstances surrounding [[spoiler:his use of the True Power]] could be considered explanation enough without resorting to this trope -- he had been undergoing SanitySlippage for upwards of six books -- and it may even be considered a subversion considering that he pulls a complete 180 back to the side of good after an epiphany later in the same book.\\\
It's outright stated by Rand that the reason he... freezes on the inside is that now he has (against his will, but that doesn't seem to matter to him) lucidly attempted to murder ([[BattleHarem one of]]) the woman he loves. The scenario is laid out in this passage (probably to preemptively [[AvertedTrope avert]] people thinking it was the True Power):

* [[spoiler:Severus Snape]] from ''Literature/HarryPotter'' is a good example. He started out as a [[NoSocialSkills socially awkward]] but well-meaning young boy who desperately craved friendship, but due to his increasing bitterness over being bullied by [[JerkJock James Potter]] and his gang, as well as the influence of his [[FantasticRacism highly prejudiced]] friends, he began to become more accepting of Dark Magic and eventually called [[spoiler:Lily Evans]] (the only person who truly cared for him) a mudblood, alienating her from him, while (according to WordOfGod) his desperate desire for friends led him to become a Death Eater.

* In Creator/JRRTolkien's ''Literature/TheLordOfTheRings'' trying to use evil methods to accomplish noble ends always makes those who choose it eventually forget their original, good, purposes:
** Gandalf states that he would begin using the Ring out of pity and a desire to do good but that it would eventually make him another Dark Lord.
** During the Council of Elrond, Elrond states that "if any of the Wise should with this Ring overthrow the Lord of Mordor, using his own arts, he would then set himself on Sauron's throne, and yet another Dark Lord would appear. And that is another reason why the Ring should be destroyed: as long as it is in the world it will be a danger even to the Wise. For nothing is evil in the beginning. Even Sauron was not so."
** Saruman in studying Sauron and Ring lore came to envy him. He forgot his purpose in opposing Sauron and began imitating him, trying to set himself up as a dark lord.
** When Frodo offers her the Ring, Galadriel says that she would become a new Queen, not dark but beautiful and terrible and that "All shall love me and despair!" but she resists the temptation to take it.
** The Ringwraiths are said to have all originally sought knowledge, and immortality, and used their rings to become great kings and sorcerers, but eventually they became completely dominated by Sauron's deceptions, enslaved to their rings, and were just extensions of his own will with no desires of their own.
** This is even the case for Melkor/Morgoth. He started out just wanting to create something of his own and devolved into wanting to destroy everything he personally hadn't created.
** Sauron, originally Morgoth's lieutenant, originally felt the world would be a better place with the imposition of his order. Eventually he just wanted the power that came with ruling.

* Discussed in principle in the ''Literature/SherlockHolmes Classified Dossier'' by Christian Klaver, after Watson is turned into a vampire. Holmes muses that Watson was able to hold on to himself due to his exceptional strength of character, but the detective reflects that, based on what they know of vampires, if Holmes was turned himself his addictive personality would at the very least put him at risk of becoming another monster as he succumbed to the thirst for human blood, prompting him to decline the idea of joining Watson as a vampire. This idea is [[spoiler:further reinforced as Watson’s wife Mary, who was turned herself and subsequently captured Watson, has completely given in to her darker urges and is a willing accomplice to their adversary]].

* In the backstory of ''FanFic/AgesOfShadow'', [[WesternAnimation/JackieChanAdventures Jade]] absorbed the power of the Shadowkhan in order to save her family from a villain known as the [[TheChessmaster Magus King]]. But the process was irreversible, and after some time she became corrupted and tried to TakeOverTheWorld herself, leading to her being [[SealedEvilInACan sealed away]]. Now, [[TimeAbyss countless centuries later]], she's now lost large chunks of her memory.

** Completely averted with Terra in [[VideoGame/KingdomHeartsBirthBySleep the prequel]]. Through most of the game, he's ''very'' careful with his use of darkness, and never loses sight of his morals or priorities. Unfortunately, he ends up even worse off than Riku.

* ''WesternAnimation/StarVsTheForcesOfEvil''

* ''LetsPlay/WitchCraftSMP'': While Scott's initial motive for learning necromancy and soul magic and trying to win the Witch Trials is to bring his partner BackFromTheDead, as he becomes more powerful, he starts slipping towards wanting to become more powerful for the sake of it. [[spoiler:To his credit, he's confronted about it in the finale, he's able to [[HeelRealization recognize the corrupting effects]] of powerful magic and chooses to [[DePower give up on it]] as a requirement to return to his original motive.]]

* ''WesternAnimation/TheLionKing'' fanfiction ''Fanfic/TheLionKingAdventures'': Simba. He goes from a sweet, mischievous cub to an [[spoiler:evil, vicious killer. Initially, he's doing it to try to find a way to bring back the destroyed Pride Lands. However, it soon turns into a desire to become the greatest predator.]]

* ''Manga/{{Berserk}}'': It's only [[DiscussedTrope discussed]] without him in the conversation, but Guts comes to the realization that this is arguably the single ''biggest'' contrast between Griffith pre-Eclipse and Femto post-Eclipse. Both were defined entirely by their dream to rule their own kingdom, but Griffith was tempered somewhat by being ([[JerkWithAHeartOfJerk or at least pretending to be]]) a ByronicHero; he was so defined by his fear of being forgotten by time that it's what [[TheAntiNihilist causes him to come to terms with his own mortality]], [[TheUbermensch making something from his finite time on his Earth with everything he can muster]]. When he [[WhatYouAreInTheDark ultimately betrayed his own ideals when nobody but the God Hand were watching]] and became Femto, this aspect was entirely lost; he no longer had his motive to fulfill his dream, [[{{Flanderization}} becoming so utterly defined by it]] that it [[CutLexLuthorACheck made what he could have ever achieved with his newfound godlike powers]] a [[VictoryIsBoring moot point]] when its simply [[TheNarcissist never]], ''[[AmbitionIsEvil ever]]'' [[DarkMessiah enough]] for Griffith.

* ''Franchise/{{Godzilla}}'' fanfiction ''Fanfic/AbraxasHrodvitnon'': [[Characters/AbraxasHrodvitnonKingGhidorah Ghidorah]]. When it first began gruesomely murdering everything in its line of sight and [[PlanetDestroyer wiping entire planets clean of life]], it was doing so because it was desperately trying to make [[TerribleTicking the Old Noise]] -- a torturous sound inside its heads which screamed at them to kill everything -- abate for as long as possible, and it grew horrifically creative with the ''ways'' in which it killed everything because it was originally hoping that it could make the Old Noise abate ''permanently'' if it found "the right way" to kill everything. But over billions of years doing this, Ghidorah grew completely desensitized to its atrocities, which eventually gave way to Ghidorah finding ''fun'' in them. By the present day, the Old Noise has weakened with the passage of so much time to the point where it's faded to the backs of Ghidorah's [[MultipleHeadCase minds]], but it doesn't matter anymore: now Ghidorah is a vicious, bloodthirsty, omnicidal monster which gleefully kills entire civilizations and planets because it '''enjoys''' it.

* ''Fanfic/JauneArcLordOfHunger'':

* Simba in ''Fanfic/TheLionKingAdventures''. He goes from a sweet, mischievous cub to an [[spoiler: evil, vicious killer. Initially, he's doing it to try to find a way to bring back the destroyed Pride Lands. However, it soon turns into a desire to become the greatest predator.]]

* The original ''Fanfic/PonyPOVSeries'':
** There's definitely a a major example in the [[BadFuture Dark World Series]]. [[spoiler: It turns out that Discord has long been trapped in a GroundhogDayLoop by the true BigBad, [[KnightTemplar Nightmare Eclipse/Paradox]], the original Dark World!Twilight, who went [[SuperPoweredEvilSide Nightmare]] in order to trap Discord in the time loops in order to torment him forever in an IronicHell. The thing is, her original intent before the corruption was to [[SetRightWhatOnceWentWrong undo all the evil performed by Discord]], but she lost sight of that in her obsession to [[RevengeBeforeReason gain revenge on him]]; by the time she's revealed, she's [[OmnicidalManiac wiped out Dark World and everything in it]] ''several billion times'', seeing everyone but Discord and Twilight as nothing but props, becoming [[EvilerThanThou far worse than Discord]] (who himself had a HeelRealization at some point) in the process.]]
** This is a running theme with [[SuperPoweredEvilSide Nightmares]] in general: most are driven by a genuinely benevolent or reasonable goal, but the power of a Nightmare comes with going insane. As a result, the majority of Nightmares become so lost in their goal they lose sight of the core attributes of it or begin doing things that they never would've done. There's a good reason the universal reaction a purified Nightmare has upon returning to sanity is MyGodWhatHaveIDone.

* In ''Fanfic/SpellboundLilafly'', Felix prepares himself for a Samhain revel by "unrooting" himself from the material world. It's a necessary part of protecting his mind and the secrets he carries, but it leaves him emotionally adrift for months afterwards. And after he [[MercyKill consumes a tormented soul]], his magic power increases but his empathy is permanently damaged.

* ''Franchise/StarWars'': Anakin Skywalker himself from the prequel trilogy joins the Dark Side in ''Film/RevengeOfTheSith'' in order to [[LoveMakesYouEvil save his wife from dying]]. Then he starts killing [[WouldHurtAChild younglings]] and things go downhill from there. When he force-chokes Padmé Amidala, the wife in question, because he believes she's turned against him, it solidifies him into this trope.