Instead of Nezuko turning into a demon you did. You are Tanjiro's younger brother. Since you became a demon you wear a bamboo muzzle and you stay in the box on Tanjiro's back. Tanjiro, Zenitsu, and Inosuke all treat you like they treat Nezuko! (Except in this AU Nezuko died with the family)

(You're male in this! Enjoy this shitty character and AU I made! ^^)