The film opens with a brutal clash between samurai and smoke-wreathed Oni, a battle that initially goes badly for the humans. In a moment of astonishing power, Monk Gen'un [Shido Nakamura] unleashes a surge of magic to wipe out the advancing demons and save a village temple from destruction. The action then pivots to Jun Tendo [Kensho Ono], a shy teenage boy who is suddenly transported 1200 years into Japan’s past, landing him in the Heian era where a war rages between humans and Oni.
Jun is immediately thrust into a world of danger and suspicion. Bullying and self-doubt shadow him as he struggles to survive in a time and place where he feels out of place. He is swiftly pursued by an Oni, forcing him to flee into the temple garden where he encounters the truth about the ongoing conflict. Inside the temple, Gen'un and a skilled swordsman named Raiko Minamoto [Takashi Kondo] reveal the stakes of the conflict and why Jun’s arrival matters far more than he realizes. The villagers begin to treat Jun as a savior, a role that both flatters and unsettles him, and he must decide whom to trust in a world where loyalties shift with the wind.
As night falls, Oni assault the temple, and the villagers rally to defend their home. Jun learns that he carries a lineage connected to the Magatama clan and bears a birthmark on his left shoulder—a mark that can awaken the full powers of a legendary dragon named Yamata no Orochi. The moment he discovers this, Jun taps into a power beyond his own will, and with the help of Orochi, he rides the dragon as it becomes his ally and source of strength. The bond between boy and beast marks a turning point in the conflict and elevates Jun from passive observer to active participant in the fate of both sides.
A growing tension emerges as Jun encounters Mizuha [Satomi Ishihara], an Oni who defies the simple good-vs-evil dichotomy. Through her, he learns that the Oni are not merely malevolent monsters but people who wear masks that project a fearsome image. The nobles have driven the Oni from their homeland to claim the land, and now both sides feel squeezed by power and fear. Jun’s hesitation to choose sides grows heavier as he hears both perspectives, and Mizuha presses him to join their cause. Yet Jun resists making a quick decision, preferring to weigh every angle and seek a path that protects both communities as much as possible. When Mizuha latches onto Orochi and escapes with Jun, the two are halted by a mysterious anti-Oni barrier that defeats them, forcing Jun to regroup with Raiko’s fellow swordsmen, Tsuna and Kinta, who have been searching for him.
Gen'un’s true schemes begin to come into sharper focus as a councillor at the temple is revealed to have been manipulated by the monk in pursuit of greater power. Jun’s anger at the manipulation of his friends and their people grows, and he confronts Gen'un with the truth about his crimes. The revelation sets off a full-blown clash between Oni and humans, and Jun tries to intervene, only to be confronted by Raiko, who has also fallen under Gen'un’s control and is transformed into one of the Four Heavenly Kings—powerful god-like suits whose minds are overridden by Gen'un’s design. The battle tests Jun’s resolve as he learns more about the personal losses behind the conflict, including Raiko’s parents, who were killed by Gen'un.
To prevent further bloodshed, Jun must break the control over Raiko and his fellow warriors. He appeals to Raiko’s shared grief and memory, insisting that the man he knew would never willingly hurt his friends. This emotional door opens Raiko’s resistance long enough for Jun to reveal a crucial alliance: Mizuha hands Jun two crucial artifacts—a small gem containing his true power and a dagger given to Raiko in childhood. When placed together, they merge into a sword that becomes Jun’s conduit of strength and the key to facing Gen'un.
With the stakes clearer, Gen'un amplifies his power, transforming the Four Heavenly Kings into a single immense, monstrous form and waging a devastating attack on all who stand in his way. Sensing the gravity of the moment, Jun channels his inner resolve and calls upon Orochi to unleash its full might. Yamata no Orochi reveals its final form, and with a mighty surge of water-based power, defeats Gen'un, delivering a hard-won victory for the side of humanity.
The climactic battle concludes with a return to the present day. Jun awakens back in his school uniform, carrying the experiences and confidence he gained in the past. Though the memories of the conflict linger, he returns to his life with a quieter strength, ready to navigate the ordinary world with a renewed sense of purpose and courage. The tale ends on a note of reconciliation between the worlds, suggesting that understanding and empathy can bridge even the widest divides when one dares to listen to both sides.
- The epic threads of courage, identity, and the moral ambiguity of war are kept front and center, presenting a story that feels both timeless and immediate. The film invites viewers to consider how power, fear, and compassion shape the choices we make, and it does so with a sweeping, mythic scope that remains grounded in the very human reactions of its young hero.
