After finishing their training at the Butterfly House, Tanjiro and his companions arrived at the "Infinity Train" where they were to carry out their next mission. There, more than 40 people disappeared in a short period of time. Tanjiro, Zenitsu, Inosuke and his companions, who were accompanied by Nezuko, met with Rengoku Kyojuro, one of the strongest swordsmen of the Demon Slayer Corps. In the Infinity Train that leads to darkness, they will face the demons lurking there.