You were fighting Shigaraki, you weren't in really good shape, neither was Shigaraki, you tried to land another hit but he a shot you with an Quirk-erasing bullet, thankfully it only hit your hand, you looked up and Shigaraki was gone, you pulled out your dagger then cut off your hand, that should helped, but now you were in agonizing pain, you then headed back to U.A. you're probably going to get a prosthetic when you get there. Once you got there some students & teachers were in the hallway