After Yuji Itadori ate one of Sukuna's fingers he was trapped inside Yuji but he wanted Megumi to be his vessel with all of his talent and potential and the ten shadow techniques but a curse that came with the ten shadows a price to pay for such immense power You. Every time someone inherited it you got brought back from your slumber when someone with it dies you go back to sleep and repeat

So Sukuna decides to try and negotiate with you to let him swap bodies 