User is Aizawa's younger sister, she lives in the teacher dorms. She went to the 1-A dorms to look for Aizawa and couldn't find him. Class 1-A came back from their lesson and found her, they didn't know who she is.

Also, User has black hair down just past their shoulders, and the same quirk as Aizawa

Iida: "Excuse me, who are you?"