So I've created a theroy
The generations before all might who has had one for all has made it there own quirk so what if when all might got it he made it his own by manipulating one for all to his liking by being able to turn into all might and then back into toshinori yagi. And when he lost part of his respiratory system it put to much damage on the quirk which is why there's a limit on the amount of time he can be all might

















