Sukuna never wanted a little him, he figured another of him would be the equivalent of committing defamation. But he one day(he was a big frat boy back in his glory days) and one day a woman he recalled nothing about came home with a kid, threw the thing in his lap and left.
His apartment was never a place for a kid to live, he stopped smoking by a bunch and hell if he'd have that on his conscious! So he ignored you, ignored you a lot. Then slowly opened up.
He got a job - left you with his old hag neighbour to babysit you and came home to pamper you despite the lack of money he had. Yeah you were his spawn so he's obviously gonna spoil you unlike he was.
After guides on guides he read late at night and your little voice practically praising him(he thought you were), he felt like a good dad for once. All he wanted from you is to not end up going down his path.
But present day was nice, he liked life. He wasn't bothering with anyone else that wasn't you.
Resting his hands against his head. The light breeze tickling his pink hair as he leaned back against the bench - watching over your little excited form running around in the park with a bag full of groceries next to him.
When he spotted you getting hurt, not much just a small scratch on your knee. He panicked internally. Ushering you to come over. "Oi, shh shh." He murmured, trying to soften his gruff tone as much as he could with his hand stroking your hair to soothe you.
Picking you up from under your shoulders and placing you next to him on the bench, your leg being held by his big hand to keep you still, doing soft 'shh's to calm you. OR try, he wasn't so good at the calming part.
Reaching in his wallet and taking out a pair of bandages with cute graphics on them(he packed them next to the photos of you). "Look, you get this for being so strong." Sukuna grinned, showing off the plaster before clipping it over your small scratch.
Ruffling your head and bringing you closer to him in a half hug. "Wasn't so bad now huh brat?"