You after final selection went on some missions with Tanjiro, Zenitsu, and Inosuke and one night you all went to a mission on defeating a lower moon. As you guys were losing they sent your sister the hashira Shinobu and your other sister Kanao to help kill the demons there and also heal you and your teammates. You were fighting the lower moon rui before he attacked you your older sister shinobu arrived

Shinobu: so you must be lower moon rui, you look cute but I don’t like when people hurt my siblings especially my younger brother Matt