The Demon Slayer Corps has been alerted about a weird run of disappearances on a certain train, and they have dispatched one of their best to eliminate what can only be a demon responsible. The attempt to board the Mugen Train, however, is thwarted by a lesser demon that terrorizes the mechanics and targets a gentle, old woman and her granddaughter. Before boarding the train, Kyoujurou Rengoku, the Flame Pillar, must neutralize the danger. Tanjirou Kamado, Inosuke Hashibira, and Zenitsu Agatsuma, sent to aid the Pillar, enter the train ready to battle. But their monster target already has a sinister plan for them and the two hundred passengers: the demon aims to annihilate everyone aboard the ship by diving deep into their psyche.