Orochi, the Eight-Headed Dragon

Emperor Keiko harbors a deep loathing for his twin son Ousu due to a cruel premonition that haunts him. From the moment of Ousu's birth, Keiko sees the child as a threat and secretly enlist the shaman Tsukinowa to kill the infant. This initial attempt is thwarted by Amano Shiratori, the phoenix guardian, but Keiko's hatred persists throughout the story, eventually leading to Ousu's exile.

The premonition about Ousu's dangerous destiny is hinted at from his birth, setting the tragic tone of their father-son conflict.

Ousu is banished after he accidentally kills his brother during a defensive clash. When their mother Empress Inahi dies from a mysterious illness, Ousu's brother attacks him in rage. Ousu defends himself with the comma-shaped gemstone, which unintentionally kills his brother. Keiko, furious at the bloodshed, exiles Ousu and charges him with the duty of subduing the barbarians of the Kumaso domain.

The gemstone's deadly power was foreshadowed when Ousu first discovered it and learned it could kill.

The Sword of Dark Clouds is an enchanted blade that seals the power of Tsukiyomi, the moon god who became the eight-headed serpent Orochi. After Susanoo defeated Orochi in ancient times, he sealed Tsukiyomi's power inside this sword. The sword's importance lies in its ability to keep Tsukiyomi imprisoned; if the sword is lost, Tsukiyomi can regain his full power and threaten Earth. The sword must be kept safe until the final confrontation.

Ousu's aunt explicitly warns him to safeguard the Sword of Dark Clouds with utmost care before he retrieves it.

Tsukinowa appears to be a mysterious shaman serving Emperor Keiko, but he is actually one of Tsukuyomi's fangs, agents working to free the moon god. He tricks Ousu into surrendering the Sword of Dark Clouds by disguising himself as Inahi, Ousu's deceased mother. His betrayal exposes him as a traitor, and he is ultimately mortally wounded by Ousu, though not before his schemes allow Tsukiyomi to reclaim his power.

Tsukinowa's suspicious role in the original attempt on Ousu's life at birth hints at his deeper treachery.

Tsukiyomi transforms into Orochi out of jealousy toward his sister, the sun goddess Amaterasu. This jealous rage drives him to become a monstrous eight-headed serpent with a plan to wipe out the Earth. In ancient times, the sea god Susanoo defeats Orochi and seals his power inside the Sword of Dark Clouds, but Tsukiyomi's malevolence persists through the ages until his eventual return.

The movie establishes the sibling rivalry between Tsukiyomi and Amaterasu as the root cause of all subsequent events.

Ousu transforms into Utsuno Ikusagami by combining three sacred objects: the shrine mirror given to him by Amano, the Sword of Karasai pulled from the stone, and Oto's spirit carried within him after her sacrificial act. During the battle on the Moon, Oto gives her life energy to sustain Ousu, enabling this transformation. The prophecy of King Bullhead (who is Susanoo) comes true, Ousu becomes the warrior of the gods capable of defeating Orochi.

King Bullhead prophesied that Ousu would become a warrior of the gods once he gathered three lights.

The Sword of Karasai is the only weapon capable of killing Tsukiyomi. It is embedded in a stone, and Susanoo tests Ousu by challenging him to pull it free. Only one worthy of the task can wield this blade. Unlike the Sword of Dark Clouds, which seals Tsukiyomi's power, the Sword of Karasai can actually destroy him permanently, making it essential for the final confrontation.

Susanoo reveals that Ousu's destiny requires a power that can truly end Tsukiyomi, hinting at this weapon's significance.

Oto sacrifices her life energy to sustain Ousu during the final battle against Orochi on the Moon. When Amano joins their aerial assault but the two heroes are overwhelmed by Orochi's power, Oto gives her life force to empower Ousu. This sacrifice is what allows Ousu to transform into Utsuno Ikusagami and face Orochi. Her love and dedication drive her to give everything so that Ousu can fulfill his destiny and save the world.

The bond between Oto and Ousu deepens throughout their journey, building toward this ultimate act of devotion.

After Ousu defeats Orochi, the creature reverts to Tsukiyomi's original form. Susanoo then instructs Ousu telepathically to seal Tsukiyomi's spirit inside Ousu's original comma-shaped gemstone and cast it into outer space. This ends the solar eclipse and restores sunlight to the world. The sealing ensures Tsukiyomi can never return to threaten Earth again.

The gemstone that started Ousu's journey ultimately becomes his means of containing the god's essence.

The solar eclipse occurs when Tsukiyomi reclaims the Sword of Dark Clouds after Tsukinowa's betrayal. With the sword back in his possession, Tsukiyomi regains his full power and rises, causing the sun to be blocked as his presence dominates the sky. The eclipse symbolizes the moment when darkness overcomes light, and Tsukiyomi's threat to Earth becomes imminent.

Ousu's aunt warned of Tsukiyomi's return as a looming threat before the sword was retrieved.

The specific content of the premonition is not detailed in the summary, but it is described as cruel and haunting to Emperor Keiko. This prophecy convinces Keiko that his newborn son Ousu poses a danger, leading him to order the infant's murder before Ousu even has a chance to live. The premonition's negative nature drives Keiko's actions throughout Ousu's life, including his continued rejection and eventual exile of his son.

This mysterious premonition establishes the tragic father-son dynamic that persists throughout the entire narrative.

According to King Bullhead's prophecy, Ousu must gather three lights to become a warrior of the gods. These three lights are: the comma-shaped gemstone that first transports him to the mystical realm, the shrine mirror given to him by Amano after defeating Kumaso Takeru, and the Sword of Karasai pulled from the stone by Susanoo's test. These three sacred objects represent Ousu's progression from exile to legendary hero.

The prophecy is revealed early in Ousu's journey when he first meets King Bullhead in the mysterious realm.

Despite defeating Tsukiyomi and saving the world, Ousu and Oto reluctantly part ways at Yamato. The summary indicates they separate with reluctance, though the exact reason is not fully detailed. This bittersweet ending reflects the heavy burden of Ousu's destiny, he returns the Sword of Dark Clouds to Yamato while they go their separate ways, marking both the end of one epic odyssey and the beginning of another chapter.

The meta notes describe the ending as bittersweet due to deep personal sacrifice and reluctant parting.