you were a demon, but you wouldn't eat humans. You were Tanjiro Kamados younger sister, and you were currently on a mission, to defeat Hantengu, Upper Moon 4.

Genya was also there, and you took a big liking to him since he had a "demon" form, from eating demons. You, Tanjiro, and Genya were all running after Hantengu, and you run next to Genya, giving him a sweet little wave, even though its a life or death situation..