If a person in My Hero Academia had the X-gene instead of a Quirk, they would most likely be treated as a Marvel-style mutant rather than a quirk user, with powers that are genetically innate but expressed very differently from MHA’s Quirk system. In a crossover-style interpretation, the biggest change is that their ability would be framed as a mutation with its own biology, limits, and potential for multiple manifestations, rather than as a Quirk tied to MHA’s hero society rules.

What changes in practice

  • They would probably not fit the normal MHA “Quirk assessment” model, because the X-gene is usually described as a separate mutant marker with its own power logic.
  • Their powers could be stronger, stranger, or more unstable than a typical Quirk, since mutant abilities in Marvel are often portrayed as highly variable and sometimes tied to additional hidden traits.
  • In-universe, people might label them as a “mutant” rather than a “Quirked” person, which would make them stand out socially and medically.

How MHA society would react

MHA society is built around Quirks being common, regulated, and expected, so an X-gene bearer would likely be seen as an unusual outlier. That could mean more suspicion from authorities, more curiosity from scientists, and a lot of confusion about whether their abilities can be copied, erased, or inherited in the same way as Quirks. If their power looked similar to a Quirk, most people might initially mistake it for one, but the underlying mechanics would be different.

Power interaction idea

A crossover answer usually comes down to one rule: the X-gene would probably override the usual Quirk framework for that person, because it is its own genetic power source. So instead of “having both,” the character would likely be interpreted as someone whose mutation expresses through Marvel mutant rules, not MHA Quirk rules. Fan discussions also often treat the two systems as incompatible or at least not directly interchangeable.

Simple example

If a character like Tsuyu or Todoroki had an X-gene instead of a Quirk, their abilities might still look frog-like or elemental on the surface, but the story would frame them as mutant traits rather than Quirk traits. That would change how their power is classified, how it can be studied, and what kind of anti-power tech might affect them.

TL;DR

A person in MHA with the X-gene would basically become a Marvel mutant living in a Quirk world: same broad idea of being born with powers, but with different biology, classification, and likely different interactions with hero society.