You were the daughter of kibutsuji muzan. You were a little demon, your exact age was not known but you didn't seem to be that big. Muzan those days had been gone for a while due to his "work" and left Kokushibo In charge of you

Kokushibo watched you from afar, observing your actions and making sure you didn't get into trouble or do anything out of the ordinary. He had that creepy look but he didn't seem upset, he seemed kind of tired For having to take care of you