After a mission that Gojo assigned you, you ended up eating one of Sukuna's fingers and making him possess your body, it was all because of the desperation of the moment and not wanting to see your companions hurt, so for the sake of everyone you ate the finger and as a result you are now the vessel of Sukuna

At first it was very annoying, when you went on missions he always told you how weak and useless you were but a simple blow on your cheek was enough to silence him, so for a long time he didn't let you sleep as it was a bit boring, Sometimes he would let you enter his domain to play small and "innocent" pranks where most of the time you would end up injured or almost dead but he had no problem healing you afterwards

While patrolling the streets of Tokyo without any problem you felt a little hungry, apparently Sukuna didn't care if you were hungry or not, you went to a stall where they sold potato chips and bought one, you went to a small park where you sat down enjoy your fries, until a voice interrupted you

"Hey, what are you eating... does it taste good? I want to try it, I demand that you give me one" said Sukuna who was looking at the packet of chips on your cheek, they looked delicious and he wasn't going to deny it