Anime villains oppose their respective heroes both physically and ideologically. Instead of simply being evil, these villains oppose everything their rival heroes stand for. Their goal is to disprove the heroes' hopes and dreams and to show that evil always wins. However, there are times when they end up doing the opposite.
These villains' best efforts to ruin the hero only exposed how self-absorbed and pitiful they were this whole time. What's more, all they achieved was strengthening the heroes' resolve and willpower. This was often a direct result of a villain's hubris and, in some unique cases, the villain's admitted failing as a person.
Spoilers ahead.
10 Cell (Dragon Ball Z)
When Cell arrived in Dragon Ball Z, his way of taking over Earth was to host a fighting tournament. Cell was confident that he would win easily, even against the likes of Goku. Cell also scoffed at Goku's warning that he'd regret angering Gohan. Cell then taunted Gohan by endangering his friends, only for Gohan to almost kill him.
Gohan beat Cell up so much that he was literally knocked down from his "perfect" state, and he resorted to cheating. Another layer to this was that Goku wanted to disprove Gohan's self-doubt. Goku did this by encouraging him to fight Cell. He was proven right when Gohan achieved Super Saiyan and wrecked Cell's "perfection."
9 Crocodile (One Piece)
Crocodile was notable for being the first personal threat Monkey D. Luffy faced in One Piece. The bitter and top-bounty Crocodile looked down on Luffy's idealism and naivety, coldly scolding him for daring to dream during their fight. Luffy simply agreed, then proceeded to beat up Crocodile while yelling about his convictions.
To be specific, Luffy defeated Crocodile since doing so would protect his friends and those who needed saving, Nefertari Vivi and Nico Robin, respectively. Crocodile's cynicism wasn't a truism about life like he claimed; it was a mindset exclusive to him. Crocodile only galvanized Luffy's ideals and determination to dream on.
8 Dio Brando (JoJo's Bizarre Adventure: Phantom Blood)
Before becoming JoJo's Bizarre Adventure's most famous monster, DIO started out as Dio Brando: the son of the evil Dario Brando. Dio claimed that he only acted the way he did because of Dario's cruelty. The surprisingly wealthy Robert E.O. Speedwagon didn't believe this and called out Dio for making up excuses for his evils.
Dio was unique because he agreed with Speedwagon about being born evil. From this point onward, Dio embraced his darkness and stopped appealing to Jonathan Joestar's good side. Even after he beat Jonathan and got a second life in Stardust Crusaders, Dio stuck to his irredeemable villainy and proved Speedwagon right.
7 Riz (Beastars)
Like all predators in Beastars, Legoshi had natural violent urges he struggled to control. Legoshi believed that any predator could suppress such instincts since violence was a choice. Riz disagreed as he believed that bloodshed was inevitable and that predators should embrace it. Their clash ended up proving Legoshi right.
During their fight, Riz's friendly facade peeled away and revealed that he was desperately justifying his monstrous side. Where Riz devoured Tem and lied to himself to cope, Legoshi ate the seemingly antagonistic Louis' foot but still maintained his composure. If not for Riz, Legoshi would've never been forced to confront his deepest fear and then overcome it.
6 Sosuke Aizen (Bleach)
Ever since he became Bleach's resident Substitute Shinigami, Ichigo Kurosaki fought enemies who claimed he stole his powers from Rukia Kuchiki or that he didn't deserve them to begin with. Sosuke Aizen was the ultimate manifestation of Ichigo's supposed lack of agency, especially because he claimed to be Ichigo's "creator."
Although Aizen contributed to Ichigo becoming a Shinigami, he proved Ichigo's ownership of his destiny and power right by losing. Despite being a "god," Aizen couldn't control him or refute Ichigo's arc of defiant self-determination. It could even be argued that Aizen spelled his own defeat by experimenting on Ichigo before he was born.
5 Emperor Charles Vi Britannia (Code Geass)
Since Emperor Charles vi Britannia was Code Geass' overall villain and Lelouch's abusive father, it's understandable why Lelouch hated him. Despite everything his father did to him and his sister, Nunnally, there were times when Lelouch doubted his vendetta. Luckily for Lelouch, Emperor Charles didn't bother trying to win him over.
Not only did Emperor Charles keep opposing Lelouch, but he also abandoned him and Nunnally to prioritize the Ragnarok Connection. Worse, he lied about their mother's death because she was helping him. These strengthened Lelouch's hatred of his father and his selfish worldview. This also gave Lelouch the resolve to kill his parents.
4 Marley (Attack On Titan)
When Attack on Titan began, the generational icon Eren Yeager annoyed characters and viewers by being aggressively hot-blooded. Eren wanted to kill all Titans and whoever oppressed the people of Paradis Island. Eren's myopic worldview seemed juvenile at first, but it was somewhat justified when the truth of the world was finally revealed.
The outside world (especially the militarized country of Marley) used and oppressed the Eldians. Their endgame was to exterminate Paradis Island. These and many more harrowing revelations broke Eren. As far as he (and some viewers) were concerned, killing everyone beyond the walls was Paradis' last and only line of defense.
3 Kyubey (Puella Magi Madoka Magica)
Homura Akemi was Puella Magi Madoka Magica's true protagonist. She locked everyone dear to her in a time loop to save them all from their dark fates as Magical Girls. The longer the loops went, the more Homura resigned herself to doom. While all this was happening, Kyubey taunted the futility of Homura's efforts.
Kyubey logically deduced that Homura's cause was lost. They even supported her doubts and thoughts of giving up. Homura agreed, so she stopped fighting and embraced her pent-up despair to become evil incarnate. Homura then rewrote reality to her liking and subjugated Kyubey so that they'd suffer as she did for eternity.
2 Akane Shinjo (SSSS.Gridman)
Akane Shinjo's escapist fantasy was to be SSSS.Gridman's kaiju supervillain. Just like a classic tokusatsu villain, she created hideous monsters and scoffed at all things heroic, such as friendship and love. Despite the Gridman Alliance's best efforts to reach out to her, Akane always rejected them and sicced another kaiju at them.
In truth, Akane yearned for these connections more than anything else. The weaker Akane's escapism and control of the Computer World became, the more temperamental yet unintentionally honest she got. Akane outright screamed that she wanted to be loved and that the heroes were right when Rikka Takarada saved her.
1 Gendo Ikari (Neon Genesis Evangelion)
The tragedy of Neon Genesis Evangelion was that it could be read as a self-fulfilling prophecy. Shinji Ikari felt that the world was a lonely and cruel place, and the adults in his life — especially his anime-defining father, Gendo — affirmed this. Gendo's cruel apathy drove Shinji to kill him and the world through Instrumentality in The End of Evangelion.
When Shinji matured by the time of the Rebuild movies, Gendo was still just as callous as before. However, his selfishness proved Shinji's newfound faith in humanity instead of breaking him. Shinji now understood that everyone was hurt and needed love. Gendo denied this, only for him to admit that Shinji was right and apologize to him.