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Demon Slayer: Mugen Train Ending Explained

"Demon Slayer: Kimetsu no Yaiba" continues to dominate the anime world as one of its most popular franchises of all time — with millions of copies of the manga series sold worldwide, a record-breaking film and an anime series chronicling the adventures of Tanjiro Kamado and his sister-turned-demon Nezuko.

When the film "Demon Slayer: Mugen Train" premiered in 2020 in Japan, it became the highest-grossing anime film of all time. Building on its success, "Demon Slayer" serialized the Mugen Train Arc, with episodes airing weekly.

While the series roughly tells the same story as the film, it's both a refresher for fans and something to hold them over until the second season of "Demon Slayer" — the Entertainment District Arc — begins streaming December 5th on Crunchyroll and Funimation. The serialized arc also dropped a new episode focused on Flame Hashira Kiyojuro Rengoku's mission before he boarded the Mugen Train.

The "Mugen Train" film follows the series' core trio of demon slayers — Tanjiro, Zenitsu Agatsuma and Inosuke Hashibira — along with Nezuko, as they join Rengoku to help investigate demon activity on the train. The film's main antagonist is Enmu, a Lower Rank demon sent by demon leader Muzan Kibutsuji to kill a Demon Slayer Corps Hashira and Tanjiro.

By the film's end, Tanjiro overcomes Enmu's hypnotism to sever the demon's head after he had fused his body with the Mugen Train. Just when the battle seems over, an Upper Rank demon appears. Protecting the others, Rengoku engages Akaza in the most epic battle "Demon Slayer" has seen thus far. Before Akaza escapes the rising sun, he mortally wounds Rengoku by punching his arm through the Hashira's torso.

It's a gut-wrenching end to a beloved character, but the finale of "Mugen Train" sets up key details for Season 2, while raising the stakes for the young demon slayers and the Hashira in their quest to rid the world of demons.

An exploration of mortality vs. immortality

The final climactic battle of "Mugen Train" pits the Flame Hashira Rengoku against a powerful demon named Akaza. After the destruction of Enmu and the Mugen Train, Rengoku and the three younger demon slayers think the battle is finally over and are confused as to why an Upper Rank demon is there. And while we've seen Hashira-level demon slayers in action at various points in the first season, what ensues in the Rengoku vs. Akaza battle is an explosive, fiery nail-biter unlike anything glimpsed thus far in the animated franchise.

Aside from showing the breadth and limits of Rengoku's Flame Breathing techniques and skills with a Nichirin sword, the battle is also a metaphorical one — mortality vs. immortality. Throughout the fight, Akaza stokes Rengoku's anger and keeps attempting to convince the slayer to become a demon, because the Upper Rank Three is impressed by the Hashira's strength and resolve.

Rengoku, of course, refuses Akaza's offers, arguing that humanity and mortality is a blessing, and that it's an honor for him to fight for them. In his last moments, Rengoku has flashbacks to his childhood and his mother telling him to use his strength and skills to protect the weak. Taking his last breaths, Rengoku smiles as he sees an image of his mother behind a sobbing Tanjiro.

Why Rengoku had to die

Besides the deaths of everyone in Tanjiro's family being a catalyst for him becoming a demon slayer, the death of the Flame Hashira is the most poignant and heartbreaking we've seen so far. Despite not knowing much about Kyojuro Rengoku before the "Mugen Train" film, he was a beloved character for his enthusiasm, optimism and noble personality. With "Mugen Train" and the new episode made for the arc's series, we learned Rengoku was loud and proud of his role as a Hashira protector — and also really loved beef bento boxes.

But Rengoku's death was necessary for a couple of reasons, no matter how heartbreaking. First, Rengoku's conversation with Tanjiro about his willingness to train the young demon slayer essentially doomed him. Tanjiro is quickly becoming a highly-skilled slayer and even successfully wields the Hinokami Kagura Flame Breathing technique. Having Rengoku as his mentor would have been a bit too convenient and would have made Tanjiro into an overly-powerful protagonist too early in the series.

The Flame Hashira's death was also necessary to establish the depths of demons' powers and the terrifying threat posed by the Upper Ranks and demon leader Muzan Kibutsuji. The Hashira of the Demon Slayer Corps are the best of the best, but it was important to establish that these slayers are still human and not all-powerful. Tanjiro and the others have been saved several times thanks to the Hashira, but it was important for them to learn they can't always rely on them for rescue.

What makes a demon slayer

Moments before his death, Rengoku tells Tanjiro that he believes in the young demon slayer's sister, Nezuko, and her ability to retain her humanity despite being a demon. Rengoku, unlike many of the other Hashira demon slayers, believed Nezuko could be saved.

At its core, "Demon Slayer" is about Tanjiro's love and dedication to the only family member he has left — his sister — and his quest to turn her back into a human. The uniqueness of Tanjiro and Nezuko's situation is established in the first episode, when Hashira Giyu Tomioka tries to kill Nezuko moments after Tanjiro discovers his family was slaughtered. Nezuko quickly proves she's an exception to every rule the Demon Slayer Corps knew about demons when she defends her brother.

Despite her loyalty to humans and relative lack of bloodthirstiness, the rest of the Hashira aren't convinced of her goodness when they meet her during Season 1. But throughout the first season and especially in the "Mugen Train" film, Nezuko hones her own fighting skills and helps the trio slay demons. In the film, Nezuko is also key to getting Tanjiro to wake up from Enmu's dream-induced spell.

Demon slayers are known for their courage, strength, loyalty to humanity and their dedication to protecting the world from demons. Nezuko may not be human, but she's become a demon slayer in her own right. Rengoku's belief in the young girl, meanwhile, makes his death all the more heartbreaking.

One step closer to Hashira

The "Mugen Train" film has an underlying current of crucial character development in between the epic, mesmerizing battles and heartbreaking finale. The franchise's core trio of Tanjiro, Zenitsu and Inosuke push the limits of their skills and are forced to confront and overcome their weaknesses in order to defeat Enmu and save the train full of passengers.

Though Inosuke (who wears a boar's head as a helmet) retains his aggressive competitiveness in "Mugen Train," the film shows him easing up a bit and becoming a more attentive team player. His boar head also comes in handy by helping him avoid Enmu's hypnotism.

The opposite of Inosuke is Zenitsu, the most cowardly of the three young slayers, but one who comes through at the perfect moment with courage and Thunder Breathing skills. His skills are only seen when he falls unconscious, making him a perfect match to fight the sleep-inducing Enmu. It's also subtly noted in "Mugen Train" that his unconscious bravery is based on his desire to protect others, especially Nezuko.

Going into the Mugen Train Arc, we knew of Tanjiro's bravery and tenacity. But the film forces him to push the limits of his will to survive. In one nail-biting scene, Tanjiro is repeatedly hypnotized by Enmu, dropping into his dream sequence. To get out, Tanjiro has to cut his own neck to "die" in his dream world. On the flip side of his ferocity is kindness, as seen when he tries to save the train operator and the young children being manipulated by Enmu to kill the demon slayers.

Raising the stakes for the Demon Slayer Corps

Up until the "Mugen Train" film, we hadn't seen any of the Upper Rank demons in action. The demons Tanjiro and the others battled in sSeason 1 were all unranked demons, aside from Rui and his Spider Family. Demon leader Muzan does make appearances, but we have yet to see him at full strength in a fight.

Enmu, the main villain of "Mugen Train," is Lower Rank 1 and the last of the Lower Rank demons after Muzen kills them in a fit of rage. To take down Enmu in the film, Tanjiro gets plenty of help from his friends, including his demon sister and Hashira Rengoku. Then, with the arrival of an Upper Rank demon and the Akaza vs. Rengoku battle, the dynamic of the series changes dramatically.

Before, the series was chiefly about Tanjiro's demon slayer training and his mission to find a cure for Nezuko. With the near-death of Akaza and the killing of Rengoku, the series shifts to include a desire for vengeance and a need to better understand the demon hierarchy — called the 12 Kizuki. This will be essential in future seasons, as Tanjiro carries on the Flame Hashira legacy and fights to cure his sister. As seen in Akaza, the Upper Rank demons are clearly to be feared, with levels of power exceeding even the most skilled of the Demon Slayer Corps Hashira.

The Flame Hashira's legacy

The Flame Hashira Rengoku died valiantly at the end of "Mugen Train," with his death ensuring no one else was harmed by Upper Rank demon Akaza. Despite his eccentric, lovable personality, his battle with Akaza showed his dedication to his craft, to humanity and to the Demon Slayer Corps.

His last moments say a lot about his character, as do his experiences before he even boarded the Mugen Train. The first episode of the "Mugen Train" series shows how Rengoku ended up on the train, including saving train station workers from a demon known as the Ripper. Through the episode, we see Rengoku's bold optimism on full display, as well as his love for noodles and bento boxes.

The episode also fleshes out more of Rengoku's skills as the Flame Hashira — from his using Flame Breathing forms to catch up to the Ripper to overcoming the demon's speed and saving a grandmother from death.

At the end of "Mugen Train," we learn of Rengoku's life mission to honor his mother by using his strength for good and protecting the weak. Before passing, the Flame Hashira tells Tanjiro to "set your heart ablaze," no matter how defeated he feels.

Exploring the Hinokami Kagura

One of the key aspects of character development in "Mugen Train" is Tanjiro's exploration of the Hinokami Kagura (Dance of the Fire God), a dance and battle technique unique to the Kamado family. When Tanjiro first meets Rengoku, he asks the Flame Hashira if he knows anything about the move, as it appears to be related to Flame Breathing.

Rengoku at first says he has never heard of it, but is nonetheless willing to train Tanjiro and the others anyway, to hone their respective breathing skills. But when Rengoku kneels, dying from a demon-inflicted wound, he tells Tanjiro to seek out Rengoku's father, a former Flame Hashira. He says his father's estate holds key documents created by past Flame Hashira that could help Tanjiro's quest to understand the Hinokami Kagura.

Tanjiro first witnessed the Hinokami Kagura as a young child, watching his father perform a ritual dance in the snow surrounded by lit torches. The dance clearly made an impression on Tanjiro, as in "Mugen Train," he summons the technique's Clear Blue Sky move to sever the demon Enmu from the Mugen Train.

Setting up season 2: Entertainment District Arc

The "Demon Slayer: Mugen Train" movie saw the death of a Hashira, the elimination of the last Lower Rank demon, the arrival of the first Upper Rank demon of the series and the personal growth of the protagonists. The film also ends with the rest of the Hashira — there are eight remaining — and the leader of the Demon Slayer Corps, Kagaya Ubuyashiki, being informed of Rengoku's death.

The next season, called the Entertainment District Arc, will follow Tanjiro and the others, alongside Sound Hashira Tengen Uzui, on a mission to investigate the disappearances of some wives in Yoshiwara's entertainment district. Trailers have shown the main antagonist of the season will be the demon Daki, whom manga fans will know as Upper Rank Six.

Based on the epic events of "Mugen Train," it's safe to assume the next season of "Demon Slayer" will show Tanjiro learning more about the Hinokami Kagura and the demons of the powerful 12 Kizuki. It has also been heavily hinted at throughout the series that Tanjiro will eventually become a Hashira. With Rengoku gone, there's an opening for a Flame Hashira, and Tanjiro is developing Hinokami Kagura Flame Breathing alongside his Water Breathing skills. But, the young demon slayer still has a long way to go, and it's clear the next season will continue to build his power.