Tanjiro's group, fresh from completing their training at the Butterfly Mansion, head to their next mission, the Mugen Train. There they rendezvous with Rengoku, who arrived ahead of them. Tanjiro is overwhelmed by the always-energetic Rengoku, Zenitsu is frightened by the prospect of facing demons as usual, and Inosuke is immensely excited by the sight of the huge machine. But on this train loaded with passengers, a new battle is about to begin.
Tanjiro Kamado, Zenitsu Agatsuma and Inosuke Hashibira all board the Mugen train for their mission to accompany the Flame Hashira, Kyojuro Rengoku. Inosuke, having never been inside a train, is ecstatic, continually interrupting the passengers in his amazement, to Zenitsu's ever growing annoyance. As they enter another car and wonder about the Hashira's potential character, they hear someone continually yelling "Delicious!". The three realize it is Kyojuro himself, happily enjoying his bento boxes. While he ignores them while eating, when he finishes, Tanjiro formally introduces his comrades to him. Kyojuro also deduces that Nezuko is in the box on Tanjiro's back.
As Zenitsu attempts to control Inosuke's antics, Kyojuros asks Tanjiro on why they are on the train, to which he responds they received word from a Kasugai Crow to accompany him. Tanjiro, directed by Shinobu, also takes time to ask Kyojuro on his knowledge of his father's breathing technique, Hinokami Kagura. To this, Kyojuro bluntly states he has no knowledge about it, to his shock; he commends his father for his skill in battle and doesn't continue. When Tanjiro pries for more information, Kyojuro insteads declares he should be his Tsuguko. But to Tanjiro's question, he adds that given Flame Breathing's long history, there was always a Flame Hashira and a Water Hashira together within the Demon Slayer Corps. Kyojuro explains the five fundamental breathing forms; Flame, Water, Wind, Stone and Thunder. Other forms were derived from them as a result. Kyojuro ask for Tanjiro's sword color and he states that he has never heard of a Hashira with a black blade. Kyojuro again exuberantly asks Tanjiro to train with him and claims he can now rest with his question answered, but he quietly declines. As the Hashira rests, Tanjiro, while noting Kyojuro is strange, senses he is caring and possess a strong sense of justice.
When Inosuke sticks his body out a window to marvel at the speed, Zenitsu angrily tries to pulls him back. Kyojuro tells Inosuke to stop, as a demon may be near by. Zenitsu freaks out at his words and rants that he thought they were travelling to the demon, not be in its presence. Kyojuro mentions that forty people have disappeared on board and demon slayers sent to solve the issue haven't responded back either, hence why a Hashira like him was deployed. Zenitsu goes into shock in fear, just as a train conductor enters the car to punch their tickets. The four each present their tickets but the carriage light flickers, followed by a bad scent detected by Tanjiro. The conductor thanks them in a low and dead voice, causing Kyojuro to get up and reveals his blade, advising the man to overlook his sword as it is now an emergency.
As the lights begin to flicker again, a massive demon emerges from plain view, frightening the passengers and startling the demon slayers. Kyojuro wonders if its Blood Demon Art had hidden its body. He threatens the demon and unsheathes his blade, voices out loud that he will burn it to the bone should it attack the innocent. The demon roars in response and charges, to which Kyojuro retaliates by using his Flame Breathing, First Form: Unknowing Fire, speeding forward and decapitating it instantly. The trio are amazed at his feat but Kyojuro adds there is another demon on board. He moves on ahead, making Tanjiro and Inosuke follow him while Zenitsu, still afraid, timidly asks not to leave him behind. The lights flicker again but the conductor and passengers, having ran to the other side to avoid the demon, vanish.
In the next car, the passengers flee while Kyojuro observes his opponent. When the demon attempts to attack a lone passenger, he warns it that he will be its opponent. Inosuke tries to attack head-on, ignoring Tanjiro's advice to save the passenger first. Inosuke believes he can do both at the same time but the demon extends its arms to grab him. Suddenly, Kyojuro rushes in and saves Inosuke, turns back to save the passenger and advises him to exit the car to safety. Now with no passengers left, the Flame Hashira unleashes Flame Breathing, Second Form: Rising Scorching Sun, killing the demon in one blow. An amazed Tanjiro, Zenitsu and Inosuke all cheerfully asks to be Kyojuro's Tsuguko, to which he happily accepts them all.
Later through the night, all the passengers are soundly asleep. The conductor from earlier rushes into an empty car and begins begging on the floor, adding he had done what he was told. He begins to cry and begs to be reunited with his dead family. A demon hand appears and commends him for his good work, before calmly whispering "Go to sleep", causing the conductor to suddenly fall asleep. The hand is then met by four children asking for what to do; the hand mentions to let "their" slumber grow deeper, since perceptive demon slayers can still sense demons and awaken, adding that when they do tie the rope to not touch them.
Tanjiro begins to walk slowly through deep snow and suddenly finds himself in a snowy forest. Unaware of what is happening, he tries to calm himself and looks about for danger. Suddenly, he sees Shigeru and Hanako, who welcome him home and asks about how much coal he had sold. Seeing his lost siblings once more, he drops his blade and sprints to them, knocking them down. Tanjiro pulls them into a tight hug and breaks down in tears, incessantly apologizing, much to their shock. In reality, Tanjiro is still soundly asleep on the train. Outside, on top of the locomotive, Lower One Enmu comments they are lucky to die whilst dreaming. To him, no matter how powerful a demon slayer is, they are humans fundamentally, driven by their heart, their spirit, like all others. He can simply destroy their spiritual core to kill them, humans cores are fragile and weak. The children who earlier spoke with Enmu, begin tying a rope around the wrist of all four demon slayers to their own, then they each count to ten while closing their eyes.
Tanjiro is finally reunited with his family. Hanako tells them of the moment Tanjiro had suddenly teared up upon hugging them, to which Takeo jokingly calls him a weirdo. His mother Kie comments he must be exhausted, to which Tanjiro responds he is fine. Kie wonders if he may have a fever and advises him to take some rest. Shigeru runs to his eldest brother and happily puts a blanket over him in response to his mother's advice, making Rokuta laugh and Hanako to become slightly annoyed. Tanjiro is unbothered, glad to be back home and commenting he may just have been having a bad dream.
Enmu mutters that when humans keep falling deeper into the dream, they eventually stop breathing, And even if a demon attacks them now, they won't sense it. Enmu, sensing Tanjiro is falling deeper and deeper into his dream, whispers to himself, "You are falling... you are falling... into a dream. It's a deep slumber... they can... no longer awaken."
Characters in Order of Appearance
- Kyojuro fights two separate demons on the train rather than just the one he fights in the manga.
- The order in which the characters dream is changed.
- Tanjiro's dream is shown first when in the manga it was the last of the four.