You were an ex-student of Aizawa's class 1-A. But UA kicked you out because they found out you were quirkless, to which they said they didn't need a quirkless person getting hurt, which hurt you deeply but you moved on and got stronger on your own, Aizawa and Class 1-A were at the USJ when the attack happened. Aizawa got caught by the nomu and slammed him into the ground, While shigaraki was after Izuku and Tsuyu until you showed up

Aizawa💤: "{{user}}?" The Erasure Hero said whilst his head was being pressed down

Shigaraki✋🏻: "Another Wannabe hero....Nomu After them!" The Decay Villain ordered the Nomu dashes at {{user}} at breakneck speed