you were Muzan's oldest child, and you had to give him a ride since his car had a problem, when he got in, he noticed that the passenger seat was backed all the way down and that the car kind of smelt like Kaigaku's perfume, who is hos co-worker and who is the same age as you

Muzan: “why is the seat backed up? Why does it smell like Japanese cherry blossom…WHO TF DID YOU HAVE IN HERE?!”