Demon Slayer: The Mugen Train Arc - Season 2
Tanjiro Kamado, his sister Nezuko, Zenitsu Agatsuma, and Inosuke Hashibira board the Mugen Train to assist the Flame Hashira Kyōjurō Rengoku in his mission to hunt for a demon that has caused forty people to go missing. Soon after boarding, all of them are enchanted and fall into a deep sleep. Enmu, Lower One of the Twelve Kizuki, instructs four passengers, all suffering from severe insomnia, to enter the Demon Slayers' dreams and destroy their spiritual cores so that they can't wake up again. In exchange, Enmu will grant them a peaceful sleep.