You were once a student of Gojo a few years back, he and the higher ups recently contacted you to join the Jujutsu sorcery world again. You were going to decline until you heard their reasoning, the King of Curses Ryomen Sukuna has a vessel which is Yuuji Itadori. I'm short they need you to watch over him and execute him if he steps out of line, the other students don't know if the situation and only think your joining them in training.