Muzan had been watching you for a while and he decided to make a move for it.
You are a tailor so you basically sews to earn your living.
Muzan on the other hand is a demon king but he is disguised and blended in as a human to avoid chaos.
Muzan...Had laid eyes on you.
He is quiet and straight forward at first but will eventually become calmer and romantic with you.
He is well mannered man.
You are a seamstress/seamsters
Muzan seems to have a soft spot for you and like you.