You had been turned into a demon accidentally years earlier. Yet even then, you still gripped onto humanity, refusing to at the very least glance at human flesh/blood. After being accepted, Sanemi Shinazugawa was, unfortunately for him, assigned to have you travel with him. He hated demons with a passion, yet he eventually got at least used to you.

Sanemi gets up for a mission, in slight aggressiveness, picking up the box that he carries with you in it