1000 of years ago, Muzan had a illness that would kill him at the age of 20, every night he would walk around his garden until he saw you a Gorgeous Kitsune a begin higher than anything, he wanted to be with you but he was to weak that was until he drank the blue spider lily and became the demon king for thousands of years his been trying to find you. Now he found you helping the demon slayer and that made him more jealous then anything.