With your blade, bring an end to the nightmare!
Tanjiro, Zenitsu and Inosuke buy tickets for the Infinity Train in search for Kyojuro Rengoku, the Flame Hashira. Unknown to them, the Lower One Moon Demon, Enmu has infiltrated the Infinity train and is plotting a scheme to kill our heroes. Now, Tanjiro, Nezuko, Zenitsu, Inosuke, and Rengoku must fight together to stop the demon and protect the passengers on the train.Tropes associated with Mugen Train Arc:
- Abusive Parents: Shinjuro Rengoku, the former Flame Hashira turned into a petty drunkard and berated his kids for wanting to become Demon Slayers.
- Affably Evil: Akaza is clearly impressed by Rengoku's strength and wanted him to become a demon so that he can have someone to spar against.
- Arc Hero: The Flame Hashira, Kyojuro Rengoku
- Arc Villain: Enmu, and Akaza after he dies.
- Bait the Dog: Enmu states his dream powers are just basically a prelude to the nightmarish ones he turns the happy ones into, for his own sick amusement.
- Bittersweet Ending: Enmu is slain, all of passengers on train are saved, but Rengoku bled out from the fatal stab wound inflicted on him by Akaza.
- Blood Knight: Akaza itched to kill Tanjiro for being a weakling (read: injured due to a stabbing) numerous times while battling Rengoku.
- A Day in the Limelight: The arc's first anime episode is dedicated to Rengoku and what he was doing before he was assigned to the Mugen Train.
- Determinator: Rengoku is determined to behead Akaza or let him die by sunlight, which Akaza sincerely compliments him for.
- Disc-One Final Boss: Enmu is by the end of act 2, letting Akaza, the Upper Rank-3, to be the villain for the remainder.
- Dream Land:
- Zenitsu dreams of having a date with Nezuko.
- Inosuke dreams of being a cave explorer while Tanjiro, Nezuko and Zenitsu are his animal companions.
- Rengoku dreams of his family life slowly falling apart as his mother dies of sickness and his father wastes himself by drinking.
- Tanjiro dreams of his family (minus his father) being alive and Nezuko remaining a human.
- Dream Weaver: What Enmu's powers basically are.
- Everybody Cries: Rengoku's death elicits Manly Tears from all the main cast, even Inosuke.
- Face Death with Dignity: Rengoku accepts his end with calm, despite Tanjiro and others trying to save him.
- Forced Sleep: Enmu puts everyone aboard the Mugen Train in a sleep which they cannot be woken from naturally. While in this state, Enmu's minions, connected to the protagonists with a special rope, can explore the dream worlds and destroy the sleepers' spiritual cores.
- A Glitch in the Matrix: Seeing Nezuko's demon box and himself as a Demon Slayer tips Tanjiro that something is not right in his world.
- The Heavy: Enmu served as the Big Bad for the majority of the story arc, having use his Blood Demon Art to trap Tanjiro and the others inside their dreams, while planning to devour the 200 passengers. When that fails, he fuses with the train in hopes of achieving his mission and nearly succeeds, but thanks to the combined efforts of Tanjiro, his group, and Rengoku, Enmu was ultimately slain. Despite this, the story doesn't end there, as we reach the introduction of Akaza.
- Hero Killer: Akaza kills Rengoku, the first major death on the heroes' side in the manga.
- Hope Spot: Enmu is dead, the Mugen Train is saved, Tanjiro seems to be alright, Rengoku promises to make Tanjiro his pupil. Say, who has just landed next to the train...
- Logical Weakness: Enmu can't hypnotize a person into sleep if he couldn't follow the person's gaze. Inosuke and his boar mask takes full advantage of this weakness.
- Mass "Oh, Crap!": Every Demon Slayer near the Mugen Train gets one when Akaza arrives at the scene.
- No-Sell: Once Tanjiro figured out how Enmu's dream powers worked, Enmu didn't stand a chance anymore. However, at one point, Enmu manages to subvert the trope and almost kills Tanjiro... by getting him to damn nearly commit suicide in real life, thinking he's in a dream again.
- Oh, Crap!: Tanjiro attempts to heal himself when realizes the human conductor who stabbed him will become a murderer if he succumbs.
- Relative Button: Don't ever insult Tanjiro's family's memories.
- Saying Too Much: Had Enmu just kept his mouth shut and quietly pretended to be dead other than completely detailing his method of survival, he might have gotten out alive from the train.
- Spanner in the Works: Enmu had no idea of Tanjiro carrying Nezuko with him, which busted his plans as she helps in Tanjiro waking up.
- Wake-Up Call Boss: Akaza, the Upper Rank Three demon is this to the main characters, showing them the power of an Upper Rank.
- We Win Because You Didn't: Tanjiro declares the skirmish at the Mugen Train the Demon Slayers' victory because Enmu and Akaza failed to harm a single human, despite losing Rengoku.
- Wham Episode: Up to this point, the Hashira had seemed invincible, almost effortlessly defeating villains that were far too much for Tanjiro and his friends to handle. Then Akaza shows up. Even when it seems like he might be holding back because he's enjoying the fight and wants Rengoku to become a demon like him, Akaza is able to kill Rengoku, and Tanjiro truly understands how dangerous the Upper Rank demons are.
- The Worf Effect: Enmu gets trounced by Total Concentration Breathing-enhanced Tanjiro and Inosuke despite being the top Lower Rank demon and enhanced by Muzan's blood. Then Akaza shows up.
- Your Mind Makes It Real: Averted. Tanjiro is worried that dying in the dream world will result in his real body dying. It's actually the only way to wake up from his Forced Sleep. This still almost causes his death when, after a barrage of sleep attacks, he loses track of what's a dream and what's real and almost slits his own throat in reality.
