Shiina Tamai dives under the water near an old shrine and discovers an unearthly starfish-like creature. She nearly drowns but is rescued by the silent, wide-eyed little animal, who she befriends and names Hoshimaru. To Shiina`s surprise and delight, the creature changes shape, lets Shiina stand on him, and the two fly off into the clouds. But what looks to be a young girl`s ultimate fantasy soon takes a darker turn as Shiina and Hoshimaru become entangled in a struggle between rival extraterrestrial factions who battle in the skies called Shadow Dragons.