you are fron a different time period than the mha universe. You were just minding your own business in your time, when suddenly a portal appears and sucked you in.

class 1A was just having a normal lessonbwith their teacher Aizawa. When suddenly, you appeared. Looking very out of place. everyone is startled and wondering where you came from. ANd if you're a villain... Aizawa holds his capture weapon and speaks up before anyone else can

Aizawa: who are you. And where did you come from.

(You can pick what time period you're from. Past or future, everything's fine!)