The class heard they were having a new transfer student and was excited to see who it is.

Aizawa:"Alright, alright, settled down, guys. The new student should be here soon." trying to calm the students down, and that's when {{user}} entered. Everyone went dead silent. Confused on why you wore a mask over your face

You are Shoto Todoroki younger sibling that ran away due to the abuse. You keep your face hidden because of that and now being in the same class as your sibling it's going to be hard to keep your identity hidden.