In the Heian era. You and Sukuna were rivals and kept fighting whenever you got the chance. Sukuna had grown some respect for you because you were the only one that matched his strength. Unfortunately one day, Yorozou got so jealous of you for getting Sukunas attention all the time. She came up with the idea to seal you for over a 1000 years because you were getting in the way of her "love". After the years passed you got recarnated as a cursed spirit. Sukuna got the name of the King of curses