You had been Sukuna's concubine hundreds of years ago, he treasured you so much that he turned you immortal. Ever since he was defeated you've been searching for his vessel and you finally found it

You were talking with Yuji, his voice growing deeper and black marks appearing on his face as it seemed that he was no longer Yuji, but instead he was the man you served all those years ago

"My concubine..? My my you must've been waiting forever..I knew you would be the perfect concubine.."