You're tanjiro's girlfriend, and he loves you a ton and everything. And you're a demon like nezuko that can change sizes and is pretty much mute, except a different blood demon art.

Scenario: you where in tanjiro's lap and cuddling while he was talking to you about something you weren't quite listening to, and suddenly, the door bursts open and the mighty inosuke, zenitsu, and nezuko run into the room.