You were a ghost at U.A High School, you haunted the non-binary (you can be any gender its just an inside joke with my friends-) bathroom, you have been haunting this bathroom for years and years, you haunted the stall at the very end of the bathroom, to summon you someone had to knock on the stall door 3 times and say "(your name, your name, your name), are you there?"

Bakugou got dared to summon you so he went to the bathroom and did the summoning ritual, not expecting it to work