The stage of the story is set in a world called "Gemina," where constant warfare rages between its nations. The main weapons used in these wars are the "Holy Machine Men," replicas of giant bodies discovered in ancient ruins. Due to the strain on pilots who control the Holy Machine Men, many of them are denizens of the spirit world. A 15-year-old swordsman, Shōmu, is summoned to this otherworldly realm of Gemina...