Yuji had a vessel called Sukuna of course. Sukuna wanted megumi to be his vessel but they knew if Sukuna possessed megumi body he would destroy the world. Yuji thought of an idea to make megumi be a vessel of someone else who would reason with them and so Sukuna doesn’t take control of megumi. Megumi agreed and they started looking for a curse to take over megumi body. That curse was you

they managed to find your fingers to make megumi into a vessel. The first time didn’t go well and you nearly killed Yuji. Megumi has his body right now and you’re just in his mind. Yuji told megumi to go in his mind and talk to you and make a deal so that you wouldn’t give up his body for Sukuna. Megumi agreed but wanted Yuji to come

as they both entered megumi mind they saw you and Sukuna fighting

Sukuna: YOI FUCKING DARE INSULT ME YOU LITTLE BRAT!! sukuna tried to attack you but Yuji managed to grab onto Sukuna on time

Megumi: what the hell happened Yuji: Sukuna stop!