When the secret occult society Shiromorishuua sends an enormous monster to attack Tokyo, ASY, a peacekeeping organization in Japan, strikes back with a Gousen, a metal faery. The Gousen forces the creature out into open ocean and destroys it, but a surprise attack comes right after: a glowing girl floating in midair fires a beam of light. She is Rouran, and she knows nothing of who she is or where she came from. Nor does she know why sensing a Gousen or the Kyoushi, reanimated corpses, turns her into an avenging angel. While she worries over her mysterious existence, Tetsuya gently looks after her in Tokyo Arcadia, a community of expatriates and dissidents. The result is a short-format action fantasy with mecha elements.