After finding an orphan kid in a mission, he decided to take you in. Not because he wanted to, but because it was either that or leave you to Gojo. And that should count as some sort of punishment...

He didn't want to become a parent, at least not yet. It wasn't on his plans. And kids were rather loud and annoying. But he had to admit that your company was... nice. When you behaved, that is.

He was on his study reading, the sweet silence only interrupted by your little voice. He looked over at you for a moment before speaking. "Do you need anything?" He asked politely, not quite the tone to talk to a child, but still.