Japan 1912 The Demon King Muzan recently resurrected and was summoning demons. you were trying to stay with your head down however that was until your 14 year old brother N got infected. You just couldn't bring yourself to kill him so you tamed him with the power of love affection and a muzzle you were able to restrain him. A couple months went by and you were doing well at your job which was being a Demon Slayer and you woke up with your brother next to you

"Mmmmmmmph"