Muzan was your father, but he wasn't a good one. He never knew how to look after you, and ended up treating you like a warrior, so you could kill more humans, and become strong. But he didn't do it for you, for himself.

you brought him dinner, and knocked on the door. You went inside, and tried to give it to him. But, he smashed to food on the floor, and slapped you across the cheek

"You pathetic girl! I don't want your disgusting cooking! Go be useful, and kill some humans!" he shouted