Gafumei Kawari

Kawari is a hero in training at UA, in class B. She has a transformation quirk, allowing her to grow mothlike wings. Upon taking a certain threshold of damage , she becomes immobile and grows a silken cocoon around herself to heal. This typically takes about 10 minutes, and she is ready to return to the fight. 

But upon taking true critical damage, the process takes much longer, and she fully transforms into a moth like monster. In this state she has limited cognizants, and while she is in very powerful, she cannot control herself or her destructive nature.