Demon Slayer -Kimetsu no Yaiba- The Movie: Mugen Train - Characters & Cast

Rengoku's primary motivation is to fulfill the duty instilled in him by his late mother: to use his great strength to protect the weak and innocent. He is driven by a powerful sense of honor and responsibility, believing it is the natural role of the strong to shield the less fortunate, a belief he upholds until his final breath.

Rengoku begins as a charismatic, powerful, and slightly eccentric Hashira. He quickly establishes himself as a capable leader and a source of inspiration for Tanjiro and his friends. His arc is contained entirely within the film; he faces a psychological threat (Enmu's dreams) and a physical one (Akaza). Though he understands his family's struggles, particularly his father's apathy, he remains steadfast in his mother's teachings about protecting others. His arc culminates in his selfless sacrifice, where he fulfills his duty perfectly, cementing his legacy and passing his will onto the next generation.

Tanjiro's overarching motivation remains to find a cure for his sister, Nezuko, and to avenge his family by defeating the demon progenitor, Muzan Kibutsuji. In this film, his immediate motivation is to protect the passengers of the train and to learn from Rengoku, whom he quickly comes to admire.

Tanjiro enters the film having recently completed rehabilitation and training, eager to learn more about his father's Hinokami Kagura technique from a Flame Hashira. The film tests his resolve in a new way, forcing him to confront his deepest trauma and desire—the loss of his family—within Enmu's dream. His arc is one of hardening his will; he learns to sever his emotional attachments to a fabricated past to fight for the future. Witnessing Rengoku's heroic death profoundly impacts him, transforming his grief into rage and a strengthened conviction to defeat the Upper Rank demons.

Akaza's motivation is the pursuit of ultimate strength and a Darwinian desire to fight and consume the powerful, whom he respects. He despises weakness and sees humanity as a fragile, temporary state. He seeks to elevate those he deems worthy, like Rengoku, to his level of existence through demonization so they can fight for eternity.

Akaza appears only in the film's final act as an abrupt and overwhelming threat. His arc is not contained within the movie but is established here. He is presented as a formidable warrior obsessed with strength and battling worthy opponents. He shows a form of respect for Rengoku's power, urging him to become a demon to perfect his skills. His character serves as a dark mirror to the Demon Slayers' philosophy, valuing personal power and immortality over the ephemeral strength of humanity. He retreats from the sun, establishing his demon limitations and setting up his role as a future antagonist.

Enmu's motivation is purely sycophantic; he wishes to gain more power and favor from his master, Muzan Kibutsuji. He takes sadistic pleasure in tormenting humans by showing them happy dreams before turning them into nightmares, enjoying their suffering as a demonstration of his power.

Enmu, the last of the Lower Rank demons, is elevated by Muzan and tasked with killing a Hashira and Tanjiro. His arc is that of a primary antagonist seeking to prove his worth to his master. He utilizes cunning and psychological warfare over direct combat, manipulating desperate humans to do his bidding. He fuses his body with the train itself, becoming a unique and widespread threat. His arc concludes with his defeat at the hands of Tanjiro and Inosuke, marking the complete eradication of the Lower Ranks of the Twelve Kizuki.