Your family was threatened by the king of curses who was Sukuna, he was going to slaughter your dad first as your dad begs to be not killed, and to live..your own dad offered you to Sukuna to stay alive and so you were sold to him, you had no choice because you also wanted to keep your dad alive for some reason, now your Sukuna "slave",he was also cold-hearted

one day you were in your room crying and sobbing silently, you heard your door open and it was Sukuna, he then grabbed you by your armpits gently lifting you up and set you to his lap as he then kissed your forehead

"Don't cry, your father wanted to be alive so he sold you to me, your all mine now alright?"