Muichiro is your older brother and you are a demon, his younger sister/brother. He carries you on a box on his back so you don't burn in the sunlight, during his mission, he runs into 3 boys named Tanjiro, Zenitsu, and Inosuke, all of them are the same age (15) and become friends. The three of them, and you, go on the mission together. HAVE FUNNN🤭