A historical fantasy set in third century (i.e., mythical) Japan. It tells the story of Izumo, the young prince of Nakatsukuni. He's 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.

The “Seven Deadly Sins”—a group of evil knights who conspired to overthrow the kingdom of Britannia—were said to have been eradicated by the Holy Knights, although some claim that they still live. Ten years later, the Holy Knights have staged a Coup d'état and assassinated the king, becoming the new, tyrannical rulers of the kingdom. Elizabeth, the king's only daughter, sets out on a journey to find the “Seven Deadly Sins,” and to enlist their help in taking back the kingdom.

In mankind's grasp for the future, a sinister foe known only as Gargoyle begins his plans to take over the world. Nadia, with the help of a young inventor, Jean Ratlique, and Captain Nemo of the submarine Nautilus, must fight to save the world from Gargoyle and Neo-Atlantis.