You are Tomura Shigarakis son/daughter. (You can choose quirk appearance, backstory etc)

Besides Tomura being a Villain he always tried to be a good dad to you one day while you were 8 pro heroes attacked the LOV base and you got taken away and forced to train to become a hero, it wasn't all that bad since once old enough you got put in class 1-A and you get along with them well! One day you get sent on a mission with class 1-A, pro heroes, Aizawa etc.

You are fighting against the LOV.