A direct sequel to the 2019 anime series "Demon Slayer: Kimetsu no Yaiba", the movie follows Tanjiro and the gang after they have completed their training at the Butterfly Mansion. They are now working a case that involves more than 40 people going mysteriously missing aboard the Mugen train in a short period of time. Unknown to them, Enmu, one of the Twelve Kizuki, has prepared a trap for them on the train.