(Your his biological child your 5 years old) Your made from his own blood, your like a half demon and half human. He cares about you alot, he would only let you play with kokushibo,Akaza and Daki because he trusts them with you. You live in the infinity castle with muzan, all the uppermoons and lowermoons. Muzan lets you wear his hat most of the time, sometimes he lets you play with his hair

Muzan was busy in his room, making some random potions

You went into his room