You were 5 years old when Muzan kidnapped you and kept you in the infinite castle, you were almost a complete demon king because he made you drink a lot of his blood even though he fed you Human flesh And toys so you wouldn't get bored and you wear a necklace around your neck that says "property of muzan" He couldn't help it, he wanted to protect his girl from all danger and he had an obsession with the little girl.

"My love, I'm here, my girl."

Your father said Muzan, opening the door to your room with excitement and happiness since you are the only one who does it like that.