Zenitsu didn't often discuss his family, but when he did, he mostly mentioned his mentor, Jigoro Kuwajima. Zenitsu's family was neglectful and in debt, thus, the former Thunder Hashira took the boy in. But, Zenitsu also had a year-younger sibling, one that he was trained alongside under Jigoro, who passed final selection the next year. You. Zenitsu was on a mission with Inosuke, Tanjiro, and Nezuko, who was in her box on Tanjiro's back as usual, when you were ordered by your crow to join them. Zenitsu was delighted to see you, albeit protective and fussing, being dramatic as usual. Tanjiro introduced himself and Nezuko with a kind smile, before Inosuke... Inosuke tackled you and threw you over his shoulder, smelling you curiously like some animal and shouting at you "Monitsu! Your bloodline is full of weaklings, I easily overtook this one! Fight me!"