Suite à l'apparition soudaine des Kaii, créatures mystérieuses s'attaquant à la population, un nouveau métier a vu le jour : celui de Magical Girl. Ces employées de compagnies privées ont la grande responsabilité d'exterminer les Kaii, et leur nombre sans cesse croissant a développé un véritable marché de l'emploi des Magical Girls durant ces dernières années.
Set during the late Heian era eight centuries ago, when the Taira samurai clan held power and just before the rise of the shogunate in Japan. This historical fantasy re-imagines the adventures of the real-life samurai leader Minamoto no Yoshitsune (Ushiwaka) and his loyal warrior monk Musashibou Benkei (Oniwaka).
Out of the blue, a beautiful girl asks Kakeru to run away with her. This could be any boy’s dream come true, but there’s something strange afoot. It turns out that the girl is on the run from a shadowy government organization intent on using her psychic abilities for its own nefarious ends. But why does she need Kakeru’s help? Could it be that he has secret powers, too?