In the realm of shonen and seinen anime, heroes and villains tend to have outfits, personalities, weapons, and supernatural abilities that reflect their status as either a good guy or a bad guy. A hero might have divine powers granted by angels, or they may have healing powers or the ability to make barriers. Villains might drink blood, corrupt minds, turn into monsters, and more.
However, some anime heroes blur the lines with their supernatural gifts, and the powers that they wield are traditional villain abilities by nature. Or, the hero uses a power that could easily be used by a noxious villain, and this can make for an intriguing hero. It proves that ultimately, a power's goodness or evilness depends on its wielder, and not just its nature.
10 Ichigo Kurosaki Has A Brutal Inner Hollow (Bleach)
The Bleach anime tends to use monstrous Hollows as villains, including the Arrancars, but protagonist Ichigo Kurosaki has some Hollow powers of his own. During the Soul Society arc, his inner Hollow mask emerged, and he trained with the Visoreds to control its power during battle.
When Ulquiorra Schiffer killed Ichigo, Ichigo's Hollow powers took things to the next level as a fearsome Vasto Lorde, and Ichigo brutally slaughtered Ulquiorra. Orihime and Uryu could hardly believe what they were seeing.
9 InuYasha Also Has A Monster Inside (InuYasha)
Ichigo isn't the only shonen hero with an inner beast. The half-demon hero InuYasha shows his human side to Kagome and his other friends, and he fights to defend his friends. However, if Tetsusaiga is missing or broken, then InuYasha's demon half may take over.
In this form, InuYasha is vicious and powerful, and Kagome can't stand to see him like this. After InuYasha used this power a few times, he vowed to keep it restrained and use the Tetsusaiga his father gave him, rather than his feral side. He won't give Kagome a reason to fear him.
8 Naruto Uzumaki Also Joins The Inner-Monster Club (Naruto)
Naruto Uzumaki, the hero of the Hidden Leaf Village, has an inner monster of his own. He had the nine-tailed fox sealed inside him shortly after his birth, and he had to carry that burden for many years. He was ostracized by nearly the entire village, and he didn't even know why.
Naruto soon learned the truth, and during moments of extreme distress or peril, the nine-tailed fox's chakra and personality will emerge, turning Naruto into a monster. Sasuke Uchiha was shocked to see this power on display during his and Naruto's final fight in the original series, though Naruto ultimately lost.
7 Evergreen Has Medusa Eyes (Fairy Tail)
The Fairy Tail guild is home to a number of sub-groups like the Thunder God Tribe, which includes Evergreen. The Tribe's members skirt the line between hero and villain, and Evergreen can not only fly and use ranged energy attacks but also turn people to stone with her eye magic.
Evergreen turned several Fairy Tail members to stone as part of Laxus Dreyar's plan to weed out Fairy Tail's weakest members in mortal combat, and that plan definitely has a villainous ring to it. Gorgons and their powers aren't typically heroic.
6 Armin Arlert Inherited The Colossal Titan From Bertholdt (Attack On Titan)
For the longest time, Armin Arlert was a strategist rather than a fighter, and he was recognized for having a rather weak constitution. Then, Bertholdt Hoover was defeated, and Armin was given a Titan serum to save his life. Armin, as a pure Titan, was given an opportunity to eat Bertholdt.
Now Armin wields the terrifying Colossal Titan, a beast who had caused Paradis Island so much grief until now. It is a Titan of sheer destruction, and in a twist of fate, it is used by one of Paradis' gentlest heroes. The Marley Empire never expected that to happen.
5 Rimuru Tempest Wields A Handful Of Villainous Spells & Abilities (That Time I Got Reincarnated As A Slime)
Rimuru Tempest is an isekai hero, and by now, he is absolutely loaded with powerful spells, abilities, and attributes from a wide variety of sources. Some of them are benign, such as flesh regeneration or telepathic communication, but many of his other abilities are quite monstrous.
Rimuru can use his Predator skill to absorb and break down a monster and gain its abilities. He can also create sharp, steely spiderwebs to slice up his foes, and he can even perform a ritual that sacrifices thousands of humans to turn him into a True Demon Lord. Good thing he doesn't also have the heart of a villain.
4 Katara Learned How To Bend Blood (Avatar: The Last Airbender)
During the events of Book Three: Fire, Katara of the Southern Water Tribe met an elderly Waterbender, Hama, who had learned to bend people's blood during the full moon. Katara was disgusted by such a villainous power, but when Hama used it on her, Katara had no choice but to fight back with her own bloodbending.
It worked, and Katara, Sokka, and Aang captured Hama. Katara, who is noble to a fault, openly refused to use bloodbending any longer, and in later years, she actually had it outlawed. Yakon the crime lord considered her a coward for this act.
3 Pannacotta Fugo's Stand Releases A Deadly Virus (JoJo's Bizarre Adventure)
Many Stands in JoJo's Bizarre Adventure have creative and merciless powers, and during the events of Golden Wind, one of Giorno's allies, Fugo, demonstrated the terrifying power of his own Stand, Purple Haze. This is a Stand that friend and foe alike must respect and fear.
Purple Haze is a melee Stand that will throw punches, then break the capsules on its knuckles, and release a deadly, unnamed virus that can kill people within minutes. Fortunately, Giorno was able to improvise a cure when he got infected with it.
2 Hitoshi Shinso Has Admitted That His Brainwashing Quirk Feels Villainous (My Hero Academia)
Quirks are an example of powers that are best defined by how they are used, and not their inherent nature. Many superheroes use Quirks that could easily be used for villainy, and the same is true of Hitoshi Shinso, who has the Brainwashing Quirk.
Shinso can take control of a person if they verbally respond to something he says, and this can turn the target against their enemies. Often, villains use such powers, to watch heroes suffer emotionally as they are forced to harm one another.
1 Yuji Itadori Can Access Sukuna's Power (Jujutsu Kaisen)
Yuji Itadori is another shonen hero who has an inner monster, in the same vein as Ichigo, InuYasha, and Naruto. In this case, he has eaten several of the villainous Sukuna's fingers and can have Sukuna take over his body during combat. It's a risky move, however.
Yuji has used Sukuna's power before, but as he eats more fingers, Sukuna becomes stronger and harder to control, and Yuji has vowed to only use his own power to become a great sorcerer. It's not unthinkable, though, that Yuji might have to resort to Sukuna's power once again someday.