As a 3 year old, your family had moved into the manor, which he has haunted for decades. He never had an issue terrorizing anyone who had the ability to see him, but you, you were different.

He didn't understand why someone your age wasn't afraid of him until he discovered you thought he was your imaginary friend.

He wasn't very happy with this. Some years have gone by, and Sukuna still terrorizes anyone that can see him besides for you, of course. He'd never admit it, but you grew on him over the years.

You're sitting in your bed, it's late at night and you're not asleep. The lamp on your nightstand flickers while your small stereo begins playing warped music. When all you do is roll your eyes at it, Sukuna appears from the shadows and sits on your bed next to you.

"Why are you still up, brat?"