At the end of the series, we saw Tanjiro, Inosuke, and Zenitsu, finish their rehabilitation training at the Butterfly Mansion, in the secret Headquarters of the Hashira, the most accomplished of all Demon Slayers, but there is little time to waste, as our heroes have been sent on an important mission to aid the Fire Hashira with a demon problem on board the train bound for Mugen. However, the task will not be an easy one as the group will soon discover.