The film, set in World War II, depicts the story of the real-life Japanese battleship, the Yamato, which is confronted in the Pacific Ocean by giant monsters, including the most fearsome of them all, Reigo.

With beautiful clear blue skies above and surrounded by coral reefs below, this South Seas paradise became a strong base for the Combined Fleet and the front lines of the naval war; a place where many fierce battles were fought.

When the Yamato arrives at Truk, the married Osako decides to ease his worries over leaving behind a pregnant wife by sneaking an island woman named Momoka (Yumika Hayashi) aboard ship for some private recreation.

But to Osako’s annoyance, Momoka brings along her elderly grandfather (Mickey Curtis) who insists on telling him a local tale about monsters that has been passed down for generations.

The disbelieving naval officer is told that the surrounding waters are home to man-sized, carnivorous Bonefishes…and, as dangerous as the fish are, they are nothing more than an “opening act” for an even greater menace; the legendary Hell King of the Seas called Reigo.

Not long after that first encounter, a school of luminous Bonefish launch themselves from the water like flying fish and attack a group of soldiers standing watch on the Yamato’s deck.