Mithril, a private military group armed with cutting-edge weaponry and skilled warriors, aspires to destroy the world's terrorism and any threats to global peace. The company is driven by the "Whispered," people with intuitive knowledge and the extraordinary capacity to manufacture powerful inventions and machines. Sousuke Sagara, a Mithril sergeant of seventeen years old, has been tasked to defend Kaname Chidori, a Whispered candidate. He is told to join her high school class and get as close to her as possible in order to save her from falling into enemy hands—that is, assuming he can blend in with their classmates without betraying his actual identity. Sousuke, who was reared on a battlefield and knows very little about the life of a typical high school student, lifestyle, must adapt to a normal school life to safeguard Kaname.