In a flashback, as a giant Limbeekoon attacks a Regios, three powerful fighters wielding "heavens blade" begin to fight it. In the present, Layfon Alseif leaves his Regios to attend the academy in Zuellni. Meanwhile, Nina Antalk loses one of the members of her platoon, and is forced to search for recruits. Layfon arrives in Zuellni as two students start a fight, and cause a building to collapse on another student, Mei-Shen Trinden. After receiving a telepathic command to save her, Layfon spirits her away from the building with incredible speed. He meets with the president of the student body, Karian Loss, who forces him to enter a military arts platoon, and Nina, who witnessed Layfon saving Mei-Shen, recruits Layfon into the 17th platoon. Afterwards, Layfon meets Felli Loss, another member of the 17th platoon who sent Layfon the telepathic message earlier. That evening, Layfon recalls that he was one of the fighters wielding a heaven blade against the giant Limbeekoon in the past.
学園都市ツェルニに入学した若者レイフォンは、他生徒のケンカを一瞬でおさめ、女生徒メイシェンを救う。そのツェルニを守る小隊の中で、一番弱小の第十七小隊は、メンバー不足のため解散の危機に陥っていた。隊を率いる少女ニーナは、必死に新入生をスカウトしようとする。一方、下校途中のレイフォンは、町外れにたたずむ銀髪の美少女フェリと出会う。
