The trope of the hero turning into the villain is a great one that has been used throughout anime, and it never fails to excite and intrigue. Some of the most successful uses of this trope see the newly crowned villain become stronger and more formidable following their departure to the dark side.

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This offers not only emotional strife for the heroes who are left and must stop these newfound villains, but it also poses a great physical threat. Thus, the heroes who remain must fight their most harrowing battles against their former allies.

10 Sasuke Abandoned His Village & Trained With Orochimaru In Naruto

Sasuke from grimaces; his curse mark is visible on his neck

Sasuke Uchiha's only goal in life was to kill his brother, Itachi, and avenge his clan. He was traumatized by Itachi's massacre of the Uchihas, and he vowed to do whatever it took to become strong enough to kill Itachi. Eventually, this led him to leave the Hidden Leaf Village and join the rogue Sannin, Orochimaru, who only wanted him as a vessel.

As a result, Sasuke was a villain for the majority of Naruto Shippuden. Sometimes, his goals aligned with the heroes', and he consequently helped them out, like when he killed Danzo. For the most part, however, he was bad. Still, he had become incredibly strong, and his Sharingan was one of the most powerful in existence.

9 Griffith Obtained Incredible Power As Femto In Berserk

Griffith expressionless

Griffith was originally a hero who fought alongside the series protagonist, Guts. Griffith betrayed everyone, especially his former friends, Guts and Casca, when he became Femto, the Godhand. He sacrificed others' lives to gain ultimate power, and despite doing good in some ways, he became a villain of the highest degree.

The power his sacrifices afforded him was rivaled by none. However, the acts he committed as Femto were unforgivable, and he proved to have left the hero persona behind completely.

8 As Red Man, Deadman Wonderland's Shiro's Power Grew Exponentially

Shiro smiles with arm held out Deadman Wonderland

Shiro was experimented on and thrown into a prison called Deadman Wonderland that doubled as an amusement park. With that in mind, it made sense that she was so traumatized that she created an alter ego, the Wretched Egg, as a defense mechanism. However, the crimes she committed as that alter ego were unforgivable.

The Wretched Egg took the form of Red Man, an image inspired by a superhero she and her childhood friend and target, Ganta, used to like. Red Man killed Ganta's classmates and had him locked away in Deadman Wonderland, too. Shiro would have been unable to do that without the incredible amounts of power she had as the Red Man, though.

7 Bleach's Aizen Was Not Ignored When He Turned Out To Be The Villain

Aizen looks down menacingly

Sousuke Aizen was one of the captains of the Gotei-13, but as a Soul Reaper, he was often overshadowed and ignored. He had a gentle demeanor and a forgettable disposition. That changed when it was revealed that he had been killing captains and was a major villain.

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He betrayed everyone, especially his former lieutenant. Aizen was so powerful that he and his Espada force were able to take on the entire Soul Society. No one had any idea he was capable of such feats before his reveal.

6 Straizo Was Useless Until Gaining The Pillar Mens' Power In JoJo's Bizzare Adventure: Battle Tendency

Straizo self destructs with Hamon

Straizo helped Jonathan Joestar defeat DIO, but in Battle Tendency, he returned as a thorn in Jonathan's son's side. Joseph Joestar was forced to fight Straizo, and he barely made it out. His quick wit was the thing that saved the day.

Looking back, Straizo and his late friend, Dire, were unprepared to take on a villain like DIO, and they were not much help. However, when Speedwagon found the Pillar Men and the other masks, Straizo decided to take power for himself, making him a much more formidable enemy.

5 Pain Was Virtually Unstoppable When He Decided To Reach Peace By Any Means Necessary In Naruto

Pain looks serious

Nagato began his journey for peace as an orphan in the Hidden Rain Village. He worked alongside his best friends, Yahiko and Konan. When Yahiko was killed, however, Nagato's worldview began to shift, and he chose to reach peace through violent means.

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Using his unique powers, he created the Paths of Pain, which served as avatars each with their own unique and village-crushing abilities. At the end of the Pain Arc, he did succeed in destroying the Hidden Leaf Village. Luckily, Naruto convinced him to backtrack and save the village. This resulted in Nagato's death.

4 Jujutsu Kaisen's Yuji Itadori Turns Evil Momentarily When He Switches With The Powerful Sukuna

Sukuna smirks within his domain

Yuji Itadori himself is not evil. However, dwelling within him is the ultra-evil entity, Sukuna, a being of limitless power and darkness. Due to a deal they made, Sukuna can swap places with Yuji, taking over his body for a short amount of time. During this time, "Yuji" becomes evil and he can do a lot of damage.

When they switch, the power that is available to the possessed Yuji is mindblowing. He can destroy an entire city in a moment if Sukuna wishes to. No Cursed Spirit or Jujutsu Sorcerer (except for maybe Gojo) can rival the raw power.

3 Zeref's Attempts To Revive His Brother Resulted In Him Becoming An Immortal Dark Mage In Fairy Tail

Zeref smiling and talking To Natsu

Zeref was a good person who had a family he loved and who befriended Mavis Vermillion, a founder of the Fairy Tail guild. However, his attempts at bringing his late brother back to life ended in him being cursed. He became a Dark Mage despite his desires or intentions, and the power available to him was rivaled by few and feared by all.

His relationship with Mavis complicated things. He spent the rest of his life wandering the world and searching for an end, while destroying all in his path.

2 Sailor Galaxia Was Unstoppable In Sailor Moon

Sailor Galaxia In Sailor Moon Anime

Sailor Galaxia was corrupted by evil, and as a result, she became one of the most formidable villains Sailor Moon and the other Sailor Senshi ever faced. Galaxia was even able to take down Sailors Uranus and Neptune when they formed a plan to seemingly betray their friends to gain an opening.

In the end, they did not really kill or destroy Galaxia. Instead, they somewhat purified her, forcing the spirit of Chaos to release her. Galaxia was unbeatable by normal standards, so they chose to help her fight off Chaos.

1 Anri Is Powerful Thanks To The Saika Demon Sword In Durarara!!

Anri Sonohara holds the sword, Saika, in battle stance

The regular school girl, Anri Sonohara, found the mind-possessing sword, Saika, which then granted Anri powers beyond that of a normal human. However, there was a lot of killing and turning people into mindless zombie soldiers involved in this endeavor.

Even if Anri still protected her friends, it was hard to call her a hero when her powers came from such shady means. Still, she can keep up with her other superpowered or ultra-influential, crime-boss peers with the help of the demon blade, Saika.

NEXT: 10 Anime Villains Who Believe With Great Power Comes Great Responsibility