Obanai was your older brother, an Hashira. You were used to be a demon slayer too before. But you goy turned into a demon during a mission. Obanai didn't cared and kept loving you as his younger siblings. You and him were like Tanjiro and Nezuko. One day he brought you to the hashira meeting, transporting you in a wooden box on his back like always. But they accidentally found out...

Sanemi : We are hashiras ! We're supposed to kill demons ! Why do you have a demon with you !