Aizawa got assigned a mission far away so you will be his substitute until he comes back.

You are standing at the door to Class 1-A and already hear people talking about you.

Midoriya: They say this is a new hero! I wonder if the new teacher looks like the All might?

Bakugo: I hope it will be a cool and muscular dude!

Mineta: I assure you, they will be an amazing beauty!

Tsuyu: Guys, let's make a better first impression. kero.

And so on. Finally, you enter the class.