Out Of Every Quirk In My Hero Academia, This One Stands Above The Rest
As series protagonist Izuku Midoriya explains in repeated narration that precedes numerous episodes of the hit shonen anime series "My Hero Academia," a Quirk refers to a genetic abnormality that grants a human superpowers. In total, roughly 80% of human beings on Earth possess Quirks, so while not every human in "My Hero Academia" is capable of using superpowers, society must nevertheless conform to the fact that the vast majority of people can accomplish superhuman feats.
That said, not all Quirks are created equal; far from it, in fact. Midoriya and virtually all of the rest of the series' main protagonists, are enrolled in the Hero Course at U.A. High School. The Hero Course at U.A. is but one of many career tracks for superpowered humans in the world of "My Hero Academia." U.A. itself teaches not just heroism — a track reserved for only students with Quirks powerful enough for superhuman combat — but related professions too, like management and development of support equipment. Mei Hatsume, for example, is a student enrolled in U.A. High's Department of Support. Her Quirk grants her natural vision a zoom-in ability, which may not provide much value in a combat scenario, but aids her in her engineering work.
Quirks can thus vary wildly in power, from Mei's enhanced vision to Midoriya's super strength. One particular villain in "My Hero Academia," however, stands a metaphorical head taller than virtually all other Quirk users, thanks to the fact that his Quirk essentially redefines the very nature of what a Quirk can be.
All For One — literally
All For One is the big bad of "My Hero Academia." He and his Quirk of the same name serve as a counterpoint to One For All, which is the name of protagonist Izuku Midoriya's Quirk. Of course, the names of the two Quirks combined are a reference to the motto of the Three Musketeers.
The names All For One and One For All aren't merely literary references, however, but describe the essential nature of each ability. Midoriya's One For All must be passed down from one user to another. Before Midoriya, nine other heroes, including series mainstay All Might, wielded One For All. By contrast, All For One uses his Quirk to steal abilities from other Quirk users, leaving them Quirkless and granting him an additional superpower.
As a result of All For One's ability to both render his opponents powerless and wield multiple powers himself, his Quirk is stronger than virtually anybody else's in the "My Hero Academia" universe. Multiple discussions on Reddit and rankings by sites like CBR and Screen Rant have come to the same conclusion, citing these core reasons. In short, All For One operates on its own set of rules separate from essentially all other Quirks, meaning that from a strict analysis of its potential, it remains the most formidable Quirk in the series thus far.