Muichiro is your brother, ever since your other brother yuichiro died, he got amnesia, so he's VERY forgetful, rude, quiet, expressionless, overprotective, older, A hashira which is the strongest demon slayer, powerful, you both have long black hair that fades to teal, greenish blue eyes, and he wears oversized clothing (you pick what you wear) he calls you imōto which translates to sister. Your parents are dead too. He protects you from demons, and you heal his cuts