Taking place in a world where 80% of people are born with innate superhuman abilities, some people are bound to have more dangerous or unpredictable abilities than others. And, like all societies, there are bound to be those individuals who will look to exploit the abilities of themselves or others to meet their personal goals to gain even more power through domination or utter destruction.
And, in My Hero Academia, highly volatile abilities can belong to anyone, from scheming adults to hapless children. With so much firepower freely walking around and relatively easy to access, it's important to keep tabs on who poses the biggest threat.
10 Takeshi Bushijima's Poison Gas Forces Him To Emit A Highly Toxic Fog
One of the most potentially dangerous Quirks in the series is only briefly featured in the "Team-up Missions" manga. Takeshi Bushijima's Quirk Poison Gas forces him to emit a highly toxic fog that renders anyone who inhales it immediately unconscious. Picture Mustard's Gas Quirk without any of the limitations. Not only is poor Takeshi immune to breathing in his fumes, he becomes physically ill by holding them within his body. Against his will, Takeshi is a walking timebomb, forced to expel noxious fumes or succumb to them himself. This makes Takeshi dangerous enough as is, but if he were to lose his conscience and go rogue, his very presence would prove massively fatal.
9 Nine's Weather Manipulation Can Cause Natural Disasters
The villain Nine's Quirk, Weather Manipulation, is massively powerful, allowing him to conjure strong storms, summon lightning, and even generate violent tornadoes. With the ability to do as much damage as a natural disaster, Nine could easily become one of the most formidable foes the world has ever seen. However, so much power comes at a critical cost since using his Quirk results in worsening cellular degeneration within Nine's body. Since his body breaks down the more he uses his powers, Nine is physically incapable of using them for prolonged periods of time or pushing his Quirk to make it stronger.
8 Himiko Toga's Transform Allows Her To Impersonate Anyone By Drinking Their Blood
Himiko Toga is the reason some Quirks come with strict rules determining how they can be used. Himiko's Transform Quirk allows her to completely copy the physical appearance and characteristics of any person, including their voice and Quirk. She's required to drink the blood of her target in order to activate her Quirk, the more blood she drinks, the longer she can hold their shape. While this would probably deter most people from using their Quirk if they ever realized they had it at all, the fact that Himiko actively enjoys that aspect of her ability makes it all the more obvious why she shouldn't be left to roam free with it. While not as widely effective as other Quirks, a single saboteur cloaked as anyone they like can do a world of damage.
7 Hitoshi Shinso's Brainwashing Allows Him To Control The Minds Of Others
Class 1-C student Hitoshi Shinso is sitting on a potential gold mine when it comes to devastatingly powerful Quirks. Hitoshi's Brainwashing Quirk lets him assume control over people's minds just by speaking to them. The Quirk requires a verbal response from the target to activate, but the response doesn't need to relate to any nefarious intent to take hold.
In addition to his Quirk, Hitoshi acquires support equipment called Artificial Vocal Chords that lets him change his voice at will to trick his targets into thinking he's someone they know. This means that, feasibly, Hitoshi can take control of the minds of half a city just by saying, "hello," to anyone he passes before they realize what he's up to.
6 Shoto Todoroki's Half-Cold Half-Hot Gives Him The Perfect Balance Between Fire & Ice
It's hard to think of fan-favorite Hero-in-training, Shoto Todoroki, being capable of great evil, with his quiet demeanor and innate sense of good and wrong. However, as his estranged brother Toya "Dabi" Todoroki shows, the intense, and frankly abusive, upbringing they shared with Pro-Hero father, Endeavor, could have sent Shoto down a very different path. Literally bred to be the ultimate heroes, the Todoroki brothers share immense pyrotechnic abilities that surpass their father's notorious Quirk Hellflame. Unlike, Dabi, however, Todoroki's inherited ice-wielding abilities from his mother make him the biggest potential threat in the family. While it's a universal rule that Quirks come with innate weaknesses to keep them in check, the fire and ice of Shoto's Quirk Half-Cold Half-Hot perfectly balance each other out, allowing Shoto to regulate his temperature when he overuses either ability. This balance, coupled with his natural strength, makes Shoto virtually unstoppable since his Quirk has no natural limitation.
5 Overhaul's Quirk Can Disassemble & Reassemble Anything How He Wants
Kai Chisaki's is a walking disaster. His Quirk, Overhaul, lets him completely manipulate matter, allowing him to disassemble and reassemble any living and non-living thing any way he pleases like a sick universal jigsaw puzzle. Overhaul has the raw potential and capability to do great good in the world, like building children's hospitals and regrowing limbs. Unfortunately, deep-seated emotional issues urge Chisaki to instead use his power to do things like completely deconstructing human beings and merging his body with other people and objects to supercharge himself, enabling him to better inflict suffering on the world. Fortunately, a quick double-amputation benched Chisaki before he could do more public harm because if left unchecked, his potential for destruction is virtually limitless.
4 Thirteen's Black Hole Can Create A Powerful Vortex That Sucks Objects Into The Void
Thirteen's Quirk, Black Hole, does just as its name suggests and generates miniature singularities from her fingertips. Thirteen's ability creates a vortex that sucks whatever object, alive or no, into a vacuous void where it's immediately atomized and swallowed by the event horizon. Luckily, Thirteen is all too aware of the catastrophic potential of Black Hole and only uses it defensively in combat, careful to use it only to create distance between opponents rather than to harm. Thirteen is happy in her role as a Support Hero and mainly uses it to discard debris, but if she were inclined, world domination would be as simple as activating her Quirk and watching it go.
3 Tomura Shigaraki's Decay Can Destroy Synthetic & Organic Matter With A Touch
Tomura Shigaraki's Quirk, Decay, is already infamous for its destructive capabilities, just as Tomura is infamous for using it to wreak havoc. Born from the profoundly ingrained trauma of having accidentally disintegrated his entire family as a child, Tomura's only sense of purpose stems from using his Quirk to inflict pain on others.
Since Decay gives him the ability to destroy synthetic and organic matter with a touch, he's particularly well-equipped to do so. Tomura becomes especially dangerous after undergoing unspecified body modifications that supercharge his abilities making him a supremely powerful threat. If it weren't for the combined efforts of Japan's Pro-Heroes, Tomura's hatred and thirst for destruction would certainly prevail.
2 Deku's One For All Holds The Power Of All The Previous Users
If Izuku "Deku" Midoriya's Quirk, One For All, is the key to making the world's greatest hero, it's also the key to making the world's greatest villain. One For All's stockpiling trait makes it so that each new user to be given the Quirk also inherits the combined power of each of the heroes to wield it in the past. Since Deku is One For All's ninth wielder, he has the power of eight of the world's strongest heroes coursing through his body. Crime-fighting is a naturally messy business, and Midoriya already causes a considerable amount of collateral damage by using his Quirk to help others. If he, or another user of One For All, were to intentionally inflict harm, there are few with the power to stop him before the body count rose to immeasurable heights.
1 All For One Can Steal & Use The Quirks Of Others
My Hero Academia's chief villain is obviously dangerous. Shigaraki's infamous Quirk, All For One, lets him take the Quirks of others and store them within his body to be used or passed on at will. This alone makes All For One an immensely dangerous ability, but Shigaraki's use of it is only the tip of the Quirk's potential to reign terror on society. All For One is bad enough mixed with Shigaraki's standard fare of stolen abilities, but when combined with other Quirks, becomes downright monstrous. When merged with Quirks like Decay and Overhaul, the potential for worldwide destruction skyrockets, turning already deadly powers virtually unstoppable. All For One's nature makes for endless combinations of Quirks to be used for nefarious purposes, making it a vital well of evil that desperately needs to be contained. Or else.