Osamu and Jay are two cereal salesmen traveling for work when they encounter a barricade. Curious as to what is going on, they step out of their car and enter into a government secret. Two mysterious demon-like men have been terrorizing the military, who came to respond to a car crash involving a vehicle carrying government research material. Inside the car wreckage, Osamu finds a beautiful hermaphrodite with gold and crimson eyes trapped in a frozen chamber. Osamu shares a kiss with them through the glass before he is forced to flee the scene. Osamu and Jay interrogate Jay's father, a top researcher at a government laboratory, who reveals that what Osamu and Jay saw was top-secret, and they would likely be sitting in prison if it weren't for his influence. While Jay is ready to forget everything that happened, Osamu cannot let it go that easily. After stealing a security badge, Osamu finds where the person he kissed is being kept, and learns that their name is Kimera. Osamu wants to run away with the beautiful Kimera, though he does not know why Kimera is being held captive or what a relationship with them means for the future of humanity.

A mysterious string of disappearances on a certain train has caught the attention of the Demon Slayer Corps, and they have sent one of their best to exterminate what can only be a demon responsible. However, the plan to board the Mugen Train is delayed by a lesser demon who is terrorizing the mechanics and targeting a kind, elderly woman and her granddaughter. Kyoujurou Rengoku, the Flame Hashira, must eliminate the threat before boarding the train. Sent to assist the Hashira, Tanjirou Kamado, Inosuke Hashira, and Zenitsu Agatsuma enter the train prepared to fight. But their monstrous target already has a devious plan in store for them and the two hundred passengers: by delving deep into their consciousness, the demon intends to obliterate everyone in a stunning display of the power held by the Twelve Kizuki.

For centuries, the Demon Slayer Corps has sacredly kept the location of Swordsmith Village a secret. As the village of the greatest forgers, it provides Demon Slayers with the finest weapons, which allow them to fight night-crawling fiends and ensure the safety of humans. After his sword was chipped and deemed useless, Tanjirou Kamado, along with his precious little sister Nezuko, is escorted to the village to receive a new one. Meanwhile, the death of an Upper Rank Demon disturbs the idle order in the demon world. As Tanjirou becomes acquainted with Mist Hashira Muichirou Tokitou and Love Hashira Mitsuri Kanroji, ferocious powers creep from the shadows and threaten to shatter the Demon Slayers' greatest line of defense.

After a string of mysterious disappearances begin to plague a train, the Demon Slayer Corps' multiple attempts to remedy the problem prove fruitless. To prevent further casualties, the Flame Pillar, Kyoujurou Rengoku, takes it upon himself to eliminate the threat. Accompanying him are some of the Corps' most promising new blood: Tanjirou Kamado, Zenitsu Agatsuma, and Inosuke Hashibira, who all hope to witness the fiery feats of this model demon slayer firsthand. Unbeknownst to them, the demonic forces responsible for the disappearances have already put their sinister plan in motion. Under this demonic presence, the group must muster every ounce of their willpower and draw their swords to save all two hundred passengers onboard. As things begin to spiral out of control, Tanjirou's resolve and commitment to duty are put to the test.