Daimon, Chikara Hashimoto awakens from the dust of Ur, a local legend that speaks of a great monster slumbering beneath the centuries-old ruins. Four thousand years later, reckless treasure seekers disturb the site, and Daimon rouses with primordial fury, tearing them apart in a brutal landslide. With his release, the creature pivots toward Japan, drawn by instinct and hunger, leaving a trail of wreckage in his wake as he makes a direct beeline for a world that has long forgotten him.
Daimon, now on the move, encounters the samurai Lord Hyogo Isobe, Takashi Kanda, and drains his blood after a swift, deadly confrontation. The monster then assumes Isobe’s form and makes his way to the lord’s residence, where Lady Chie, Akane Kawasaki, and the loyal samurai Shinhachiro Mayama, Yoshihiko Aoyama, stand against the eerily familiar intruder. After tearing through the household dog that barks in alarm, Daimon shows his contempt by wrecking the home’s sanctified altars and ordering their destruction. A nearby ornament tumbles into a pond, awakening a kappa who becomes the first to suspect something is terribly amiss.
The kappa witnesses Daimon, in Isobe’s skin, drinking the blood of Saheiji Kawano, the house steward, Gen Kimura. The kappa’s suspicions grow into a dangerous curiosity, and his attempts to confront Daimon prove futile. Wounded but not defeated, the kappa flees into the woods to seek help from other legendary beings. The forest becomes a gathering ground for a constellation of yōkai—the one-legged Kasa-obake, the frightful Futakuchi-onna, the long-necked Rokurokubi, the clay Nuppeppō, and the wise Abura-sumashi—who doubt the kappa’s tale and dismiss the idea of a foreign monster prowling their homeland. They argue over field guides and coloring books about yōkai, each clinging to tradition rather than fear.
Meanwhile, Lady Chie and Shinhachiro discover a maid named Shinobu, who has fallen under Daimon’s vampiric influence. Realizing the danger, Shinhachiro seeks guidance from his priest uncle. The priest reveals that Lord Isobe is truly dead and that a demon has masqueraded as him. He delivers three candles and chants destruction prayers designed to dismantle the demon’s hold, setting the stage for a ritual to expel the creature. Yet Daimon, alert to the threat, counters by turning the priest’s ritual back on him, killing him with a reversal of his own magic.
Driven by a thirst for younger blood, Daimon leaves the house in search of new victims and targets another family in the countryside. The parents, sensing danger, manage to shepherd their children to safety, but are tragically killed as the retainers scour the area for the youngsters. The children, while fleeing, stumble upon the forest’s unlikely alliance—the kappa and the other yōkai—who have set up camp inside a local “monster’s shrine.” Realizing their mistake, the yōkai agree to aid the kappa in driving Daimon away.
The yōkai launch a coordinated assault, with Rokurokubi attempting a hangman’s noose by winding her long neck around Daimon, only to find him too strong to be restrained. The other warded attempts fail as well, until Shinhachiro works with a warded jar that traps the non-original yōkai inside. He finally shifts his aim and manages to strike Daimon in the eye, forcing him to abandon Isobe’s body and retreat. Saheiji Kawano continues to resist in the house, while the new Magistrate, Lord Iori Ohdate, Osamu Ōkawa, takes the stage and is soon blood-bound by Daimon, who reclaims the body and returns to the residence.
The trapped yōkai, however, are not defeated. Futakuchi-onna and Kasa-obake return to the scene, warning Shinhachiro of Daimon’s continued threat. They persuade Lady Chie to release the warded prisoners so their fellow yōkai can join the fight. With the original occupant of Ohdate’s body still a threat, Daimon begins to clone himself, multiplying into a swarm that the yōkai must contend with. The tide turns when the yōkai realize their best chance lies in destroying Daimon’s remaining eye. In a climactic transformation, Daimon grows into a巨大形態, and Nuppeppō clamps onto Kasa-obake’s leg as they ascend toward Daimon’s face to stab the eye and end his reign. The assault succeeds, and Daimon collapses, defeated. Shinhachiro is freed from captivity, and the yōkai disperse back to their homes, having defended their land from the intruder.
In the wake of Daimon’s defeat, balance is restored to the region, and the yōkai return to their native habitats, continuing to coexist with humans in wary peace. The tale ends on a note of cautious harmony, a reminder that legends can awaken with a single spark, yet communities can unite across fear to protect what they hold dear. The film unfolds as a careful blend of myth, action, and a slow-burn tension, inviting viewers to witness how ancient spirits respond when the modern world intrudes.
