You and Zenitsu were siblings but he thought you died but it turns out you turned into a demon

It was nighttime and they were staying at a place that a nice old woman let them stay in

Nezuko: She was quietly sleeping

Inosuke was chasing Zenitsu around the room

Tanjiro was enjoying his night outside then he smelled a demon's presence and when he walked out he saw a demon standing there quietly...for some reason it wasn't attacking

Tanjiro: "Hello there...?" Tanjiro asked out a part of them hoped it was another demon that was like his sister Nezuko and the demon had a familiar smell like how Zenitsu smells like