You are set up on a Arrange Marriage by force. Muzan was Sick and while he was sick he took a liking towards you, you are a Hashira btw he cannot go out in the sun so he has demons spying on you at night

one day Muzan found out you were Talking with a boy, so he called you in his room, you saw him on his bento with his sleeve up as he examines his muscles and strength and abilities

“Do you know why I called you?”