In the 25th century, a spacecraft carrying 300 people departs Earth seeking a new home within the solar system, but an unforeseen disaster strikes. The vessel falls into a black hole linked to another universe, and the passengers are set adrift in an emergency capsule, eventually landing on a planet called Ismo. The tale begins twelve years after their arrival on Ismo.
Ismo is a star of the Onam System, which mirrors the Solar System of our universe, and it is the only planet left in that system. The so-called Death Star Yomi is a comet that periodically draws near the Onam System.
Long ago, the Onam System had eight planets. In the age of the gods, a war was waged against the evil monster Yamatano Orochi, a serpentine creature with eight heads. The gods emerged victorious and sealed Yamatano Orochi within eight stones, each buried at the core of a planet. Access to those planetary cores was forbidden to all. Yet Tsukuyomi, the wicked god who rules Yomi, managed to reach the stones one by one, using his powerful robots known as the Sky Warriors to destroy seven planets. However, when he attempted to seize the final stone from Ismo, the mightiest Sky Warrior, Susanoo, went out of control and was blasted away.
A million years later, the Death Star Yomi once again approaches the Onam System. Tsukuyomi, Yomi's master, intends to use this chance to fulfill his ambition of dominating the entire universe. He desperately seeks the last stone that holds Yamatano Orochi, for if he obtains it, the monster will revive and its power will become his. To capture the stone, Tsukuyomi requires the Sky Warrior Susanoo, so he dispatches eight Sky Soldiers to retrieve Susanoo. But they are too late. Susanoo no longer answers to Tsukuyomi; it now belongs to Takeru, a 13-year-old boy from Earth who happened upon the buried robot and roused it from its million-year slumber. Takeru is drawn into the fight against the Sky Soldiers and their evil master Tsukuyomi, and Susanoo rises to defend his friends and their planet.
