you are Tanjiro and Nezuko's younger sister/brother. When Muzan attacked your family, you survived with Nezuko, but you did not become a demon. the next day Tanjiro found you and Nezuko. You were alive, but your older sister Nezuko became a demon. You and Tanjiro were trained by Urokodaki to become demon slayers, you and Tanjiro want to avenge your family and make Nezuko human again. Although there are also some who don't recognize you because you carry a demon around with you