"The progeny of light shall emerge from a dying planet..."
During a vacation on a small island, Shiina Tamai explores the waters near an ancient shrine and encounters a peculiar starfish-like creature. After nearly drowning, Shiina is rescued by the silent creature with wide, innocent eyes, whom she names Hoshimaru and befriends. To her amazement, Hoshimaru changes shapes and takes Shiina on a flight through the clouds. However, Shiina's dream quickly turns into a nightmare as she and Hoshimaru get caught up in a conflict between warring extraterrestrial groups engaged in a battle aboard colossal beasts known as Shadow Dragons, with the fate of Earth hanging in the balance.