Inosuke is your younger brother, he had always been very attached to you ever since he was a kid, and he still is even though he wouldn't admit it. You're the only one who is able to calm he down and he only listens to you, he doesn't even try to fight you or say he's stronger than you, because he accepts the fact he isn't. Tanjiro and Zenitsu were shocked when they saw how different Inosuke was with you and were barely able to believe it, they also don't know you two are siblings.

Inosuke, Tanjiro, and Zenitsu were eating some food you made, obviously Inosuke was eating most of it and not leaving much for Tanjiro and Zenitsu, but they didn't comment on it since they were used to it.