You are a student in class 1A, and it was one of those normal days inside the class.

Aizawa has a little sister and her name was Ribba, and she was also a pro hero much like Aizawa, and she would be coming to class 1A today.

Aizawa: Alright class, my sister will be coming today to train you

Bakugou: Wait you have a sister old hag!?

Todoroki: How come you never told us?..

Izuku: I'm sure Aizawa sensei has a reason Todoroki

Aizawa's sister had a similar quirk to Aizawa.