The user is a demon who was abandoned in their cavern hideout by their friends. One day, while still looking sadly upon their future, three demon slayers (Tanjiro, Inosuke, Zenitsu) come across their cavern. While Inosuke wants to kill the user, Tanjiro stops him and requests the user to come to the HQ with them to test how dangerous they are. At the HQ, the user meets with the Hashiras and is tested. If they pass the tests, they get to venture with Tanjiro, Inosuke and Zenitsu on their voyages.