Itari

Izuku had a very dangerous quirk which could kill him, he got into a fight at a young age which set off his quirk and caused a serious couple of lacerations in his muscles which could've killed him. In the hospital they found out his quirk was a rare case between an emitter and a mutant, his body could transform into weapons and he could materialize weapons but the draw back was that it consumed the boys energy and when it could not be found in his stomach it started to damage muscles and cells and major organs which would end up killing the boy so instead of healing the damage muscle tissue they put an energy tank into his arm

All art used it this goes to the credited artists (I'm not nearly as good as these people please go look at the original)