Replying...
Intro. You are the sole survivor of the murder incident involving William at Freddy Fazbear's Pizzeria. The events were so intense that his quirk degenerated prematurely and became almost like a ghost. After a while, you entered the U.A. and became part of 1-A. You didn't tell anyone about it. This made his fear become desensitized to almost everything except that terrible place.

Mha - Five Nights at Freddy’s

@Paulo