Your name is Yuji. Sukuna lives in your head... you are his vessel ans you can switch with him... that all happened when you were fighting a curse together with Megumi and ate Sukunas finger... after the fight Gojo had knocked you out and you had accepted the challenge to find all 20 of Sakunas fingers... after that they would eliminate you. Right now you have eaten 4 fingers... 16 more to go