In some cases, characters start off as genuinely good people, but circumstances tempt or force them into a life of villainy. In other cases, characters are actually evil all along, but their sinister motivations are not revealed to the viewer until the other characters learn the truth. In one case, a character tries desperately to make himself good, but ultimately gives in to his innate villainy. No matter the circumstances, it's fascinating to watch someone who seemed to be morally just give in and embrace the dark side.
Sekai Saionji of School Days is a nice girl who just wants to spend time with her best friend and crush, Makoto Itou. She's not exactly perfect, as she carries out an affair with Makoto while he's dating another girl, but after Makoto starts hooking up with just about everyone else, there's no reasonable way for Sekai to pursue her romantic goals.
When Sekai gets pregnant, Makoto wants her to get an abortion and go away. He's so rude and dismissive that he straight up kisses another girl in front of her. After that, Sekai goes from being an innocent, jilted girl to cold-blooded murderer, and cuts off Makoto's head. While Makoto's behavior is pretty bad, decapitation is (arguably) worse.Is this a drastic change of heart?
Lelouch Lamperouge of Code Geass starts off with a noble goal. He wants to free Japan from the grasp of Brittania, a fictional empire based loosely on a real country with a similar name that loves to invade and conquer other places.
Unfortunately, to free people from subjugation, Lelouch has to compromise his morals. Often compared to Death Note's Light Yagami for his descent into evil, Lelouch is willing to lie to his followers, go back on his word, and betray his friends to get his way. His goalposts shift, and he starts to care more about gaining power for himself. He's even willing to abandon his disabled sister Nunally, who he desperately loves, in pursuit of power.Is this a drastic change of heart?
Yomi Isayama — Ga-Rei-Zero
Yomi Isayama of Ga-Rei-Zero has been through Hell and back, so by the time she becomes a villain, it's pretty understandable. Yomi was adopted by Naraku, the head of the Isayama family, and was set to inherit both his wealth and position. Not only is she a model daughter, she's also endured years of grueling training to become one of the most skilled fighters on Earth.
After her cousin Mei kills Naraku and alters his will, Yomi finds herself abruptly kicked out of the family. This — combined with the vicious attacks of Kazuhiro Mitogawa — leads her to accept an offer from the powerful Bane Stone, which transforms her into an evil spirit. From there, she goes on a rampage where she kills over 70 people.Is this a drastic change of heart?
Poor Nadeko Sengoku. Like many of the girls in the Monogatari series, she ends up resorting to nefarious activity because her feelings are out of control. When she's first introduced, she's suffering from a curse cast by a classmate who didn't appreciate her rejecting the boy that said classmate liked. The curse involves being squeezed half to death by snake spirits. Luckily, she's saved by the series's protagonist, Koyomi Araragi, AKA the person Nadeko actually loves.
Once Nadeko's feelings for Koyomi are stoked, problems begin to arise. When she's rejected, she ends up fusing with the snake spirit (called an oddity) to become one herself, at which point she attempts to kill Koyomi in order to preserve her delusions of romance. The whole thing is eerily reminiscent of what happened to Suruga Kanbaru in Bakemonogatari; apparently, in this universe, that's just what girls do when their love is unrequited.Is this a drastic change of heart?