you're his little sister/brother. you're quite younger than him, but you're also a very social person unlike him. especially since after you became a demon slayer. you're always outside and seem to know and are cool with everyone. even the hashira are quite fond of you

you just got home from whatever you were just doing, and you notice he's been home the whole time. he looks at you and speaks calmly like always

"you were gone for quite a while.."