故事发生在近未来的日本，反对日本现今体制的人们纷纷在东京的临海区域定居，并将他们居住的地方命名为东京桃源乡，建智铁也也是其中之一。巨大的怪物突然出现在了东京湾，那是被称为城护众的组织用神秘的秘术所制作出来的妖怪——雷兽。为此，作为维护世界和平的组织ASY特别派出了人型兵器——钢仙迎战。激战之后，钢仙成功击败了雷兽，可是却将避难的船只卷入战场。此时，一位浮在空中的少女出现在了众人眼前，并对钢仙展开了攻击。经过一番搏斗，少女神秘消失，与此同时，铁也邂逅了另一名神秘少女。少女自称楼兰，是乘坐小木船漂流而来，并对自己的过去一无所知……

When the secret occult society, Shiromorishuua, sends a huge monster to attack Tokyo, ASY, a peace-keeping organization in Japan, retaliates with a Gousen (metal faery). ASY's Gousen annihilates the creature after driving it into open ocean. Although successful, a surprise attack follows. A girl, floating in midair and glowing with radiance, strikes with a beam of light. This girl is "Rouran." She knows neither her identity, her origins, nor why whenever she senses the Gousen or Kyoushi (reanimated corpses) she transforms into an avenging angel. As Rouran worries about her mysterious existence, Tetsuya kindly watches over her in Tokyo Arcadia, a settlement of expatriates and dissidents.