A historical fantasy set in third-century (i.e., mythical) Japan. It tells the story of Izumo, the young prince of Nakatsukuni. He is not very interested in studying, unlike his cousin Dekiru; instead, he wants to see the wider world. One day, a mysterious girl named Sanae shows up as a stowaway on an airship. Although nominally from Yamataikoku, she is actually from the Naga, a shadowy people possessing magical powers. Sanae is kidnapped by Takeru, a warrior from the rival kingdom of Akusa, and placed at the mercy of the evil witch Yomihime. Izumo, helped by an orphaned glider pilot named Navi, must now take up the sacred sword of his country, master its powers, and rescue Sanae. However, before that, he must defeat the reawakened eight-headed snake of legend, Yamata-no-Orochi.