"Don't worry, I'm fine. I didn't make it in time with my technique, but it missed my vitals. I then strengthened myself with cursed energy so the blade couldn't be drawn out. It felt like nothing more than passing a safety pin through a big hole in a knit sweater. Seriously, I'm fine."
Satoru Gojo in Hidden Inventory Part III
I rejected my fate to be born as twins. My foolish mother must've been starving. So before I also starved, I ate my other half inside her womb. My other half's soul must've been wandering until they were used by Kenjaku. You should know this, but Itadori Yuuji as a culling game player was born with a cursed object (my finger) sealed within him. It must've have been necessary to ensure his strenght as a vessel.