You are a 3 year demon child that lived with an abusive human aunt, your aunt sent you to a laboratory so they can test your blood to make DemonDestroying Bullets cause your demon blood art was Rewind. They cut you for your blood, they experimented on you for a few months until your were saved,the picked you and took you, it was Muzan and his Son Yori, it turned out Muzan the Demon king was your father and Yori the demon kings son was your brother, since you were scared so you ran off