In fiction, there are often times where heroic characters get tempted to join the forces of evil with promises of power, fame, or some other desire. While some are able to resist the allure to the dark side, others are not so inclined to refuse the call and become a new enemy for the good guys to face.

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Anime has seen its fair share of dauntless heroes who have watched friends become villains for one reason or another. And sometimes it's even that hero's best friend that switches sides. With friends like these who even needs enemies?

10 Agumon Got Captured And Corrupted By The Digimon Emperor (Digimon Adventure 02)

Dark Metalgreymon, Digimon Adventure 02

Most fans of Digimon would immediately recognize Agumon as the face of the franchise and most notably, Tai's partner in the original anime, but there have been times where this iconic Digimon has gone out of control. While Tai forcing his pal to Digivolve into Skullgreymon could be considered a moment, this entry goes to the time where he was captured by the Digimon Emperor in Adventure 02.

Mind-controlled by the Dark Rings, Agumon is forced to attack his friends and allies as Greymon and is even forced on two separate occasions to Digivolve into Skullgreymon and a darker version of Metalgreymon before he's eventually rescued.

9 Joey Was Mind Controlled By Marik To Duel Yugi (Yu-Gi-Oh!)

Joey possessed or controlled by Marik.

Yu-Gi-Oh! is no stranger to the "mind-controlled friend" plot, employing it several different times across the franchise, but the most memorable one had to be when Marik possessed Joey into dueling Yugi with both their lives on the line. During the "Battle City" arc, Joey and Téa are both captured by Marik and are used as pawns and hostages against Yugi and the Pharaoh.

Chaining both duelists chained to an anchor, Marik's plan to use Joey as a puppet almost succeeds in plunging Yugi into the dark depths of the ocean. It's only thanks to Joey regaining control of himself and Serenity making a last-minute save that made everyone come out of this one okay.

8 Heartbreak And Despair Turned Sayaka Into A Witch (Puella Magi Madoka Magica)

Madoka Magica Sayaka Smiling

In all fairness, Sayaka Miki did become a Magical Girl to save Madoka and used her wish to heal her crush Kyosuke's hand, which were selfless acts in themselves. However, this is Madoka Magica, so it could never have been as simple as just that. After learning the dark truth about Magical Girls, Sayaka falls into a deep depression.

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Things end up spiraling out of control for Sayaka, as on top of her grief and insecurities her heart is broken when one of her friends becomes Kyosuke's girlfriend. Sayaka only becomes more unstable from there, lashing out at everyone who tried to help her, even Madoka, until her despair ultimately turned her into a witch.

7 Ryo Was Actually Satan In Human Form (Devilman Crybaby)

Ryo Asuka In His True Form As Satan (Devilman Crybaby)

When first presented in Devilman Crybaby, Ryo Asuka seemed like they were the type of person who'd cross all sorts of lines for their friend Akira, but things progress their morally questionable actions become more evident as they became the true villain of the story and revealed themself to actually be Satan in human form.

While Ryo wasn't exactly the pinnacle of morality in the beginning, but they supported Akira and tried to protect him. Unfortunately, once they awoke to their true self, any shred of humanity in Ryo was gone. They only reawakened to that humanity after it was far too late.

6 Eren Turns His Back On Mikasa And Armin (Attack On Titan)

Eren from Attack on titan

After the first several seasons of Attack on Titan, it seemed like Eren would risk the sake of the world for his friends, especially Armin and Mikasa. However, once the fourth season rolled around, Eren was noticeably different, more cold and callous than he used to be. After Eren's attack on Marley, Eren begins a revolution on Paradis, one to end the cycle of violence between Eldia and Marley and big implications for the world.

As his friends become caught in the crossfire, Eren meets with both Armin and Mikasa and essentially cuts all ties with them, telling Mikasa that she has no free will and hates her, then going on to beat Armin to a pulp.

5 Vegeta Lets Babidi Possess Him To Get A Shot At Goku (Dragon Ball Z)

majin vegeta

One would not look at Vegeta from Dragon Ball and immediately think that he was Goku's best friend, but their rivalry has brought out the best in them. Vegeta may have turned over a new leaf during his time on Earth, but he backslid pretty hard during the "Majin Buu Saga".

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After Babidi turned him into Majin Vegeta, Vegeta ends up using his newfound power to kill dozens of innocent people and fight Goku. The most shocking part about all this is that Vegeta admits he could've resisted Babidi's control, but let it happen in order to get the chance to finally beat Goku.

4 Tetsuo Goes Mad With Esper Power (Akira)

Tetsuo, Akira

At the start of AkiraTetsuo's quietness hid his insecurities, but after an accident that sees him being experimented on by the government, he begins exhibiting esper powers. With these powers, Tetsuo begins to become more aggressive, not only towards those who look down on him but towards his friend Kaneda, his inferiority complex making him see himself only as his subordinate.

As the film progresses, Tetsuo becomes arrogant and mad with power, attacking anyone he pleases with sick joy until he finally loses control and mutates into a grotesque fleshy mass, eventually disappearing into a new plane of existence.

3 Sasuke Became A Rogue Ninja For The Sake Of Vengeance (Naruto)

Naruto fights Sasuke, Naruto Shippuden

In Naruto Sasuke started out with one goal in mind, to avenge his fallen clan by killing his brother, Itachi. As the series progressed and Naruto himself became stronger, Sasuke began to feel weaker and more insecure and eventually left Konoha to gain the power he needed to get his revenge.

After stopping Naruto and the others from bringing him back and training with Orochimaru, Sasuke killed Itachi and joined the Akatsuki turning his sights on Konoha itself, vowing to destroy the village in a quest for vengeance that very nearly consumed him.

2 Lelouch Became A Villain To Unite The World Against Him (Code Geass)

Lelouch dies, Code Geass

Code Geass' Suzaku and Lelouch were two sides of the same coin. While Suzaku wanted to change the Britanian Empire from within, Lelouch sought to change the world with his own two hands by any means necessary. These clashing ideals would eventually bring the two friends to blows.

Eventually, Lelouch's rebellion began to cross more moral lines and after he took over the Empire entirely, Lelouch made himself the enemy of the world until Suzaku (as Zero) killed him. In truth, Lelouch's turn to the dark side was all part of his plan, his death serving as a way to bring about peace.

1 A Broken Griffith Sacrifices His Comrades To Join The God Hand (Berserk)

Griffith makes a move during the eclipse in 90s Berserk

They do say the road to hell is paved with good intentions, but Berserk's Griffith is something else entirely. Originally, as the leader of the Band of the Falcon, Griffith's dream was to end the Hundred-Year War and bring about peace, a noble dream that was slowly snuffed out.

After Guts leaves the Band of the Falcon, Griffith becomes unstable and goes on to be captured and tortured till he's left as a shell of his former self. Completely broken, Griffith invokes the Eclipse and sacrifices his allies in order to be reborn as Femto and join the God Hand. Guts is left to watch in horror as the Band of the Falcon is utterly devastated by his former friend.

NEXT: 10 Anime Where Everybody Dies