I think kai was one of the vessels for afo, since we know the quirks afo gives aren’t always accepted by the bodies and the body tries to keep up with it by modifying itself that would explain his allergies. Since we don’t really know his life before shie hassaikai, it can be a possibility that he like dabi escaped the facility and by pure luck ran into pops. That would also explain his devotion to pops and hate for quirks maybe he like shigaraki remembers the emotions of that time-period but not the memories.
just something that’s been plaguing my mind lately.











