Tanjirou and the group have completed their rehabilitation training at the Butterfly Mansion, and they arrive to their next mission on the Mugen Train, where over 40 people have disappeared in a very short period of time. Tanjirou and Nezuko, along with Zenitsu and Inosuke, join one of the most powerful swordsmen within the Demon Slayer Corps, Flame Hashira Rengoku Kyoujurou, to face the demon aboard the Mugen Train on track to despair.