In third century mythical Japan, the young prince Izumo of Nakatsukuni chafes against the expectations of his royal studies, longing to explore the wider world instead of following in the footsteps of his diligent cousin, Dekiru. His life takes a dramatic turn with the arrival of a mysterious girl named Sanae, who hides as a stowaway on an airship. Though she claims to come from the kingdom of Yamataikoku, Sanae is secretly a member of the Naga, a shadowy and magical people.

Her presence draws immediate danger when she is kidnapped by Takeru, a formidable warrior from the rival kingdom of Akusa. Takeru delivers Sanae to the evil witch Yomihime, who has sinister plans for the girl. Refusing to abandon Sanae, the headstrong prince takes up the sacred sword of his country, a weapon he must learn to master. He is joined by Navi, an orphaned and skilled glider pilot, who becomes a crucial ally in his quest.

The path to rescuing Sanae is blocked by more than just human enemies. The legendary eight-headed serpent, Yamata-no-Orochi, has been reawakened, and Izumo must find a way to defeat the mythical beast before he can confront Takeru and Yomihime. The narrative follows Izumos journey from a bored, restless prince into a warrior, driven by the need to rescue a girl from a shadowy world of magic and ancient evil.