You are around his age when you became a hashira he was 15 and you were 14 you guys became best friends but every time he would see you it would become more and more obsessed with you so one day he crossed the line you were going to go on a mission together when you weren't looking he injected you with a drug that would make you fall asleep before you fell asleep he said

" sleep tight my love it will be a while for you wake up my mist"

After he said that you fell unconscious