In a quest to combat global terrorism and protect world peace, Mithril, a private military group, utilizes advanced weaponry and a special team led by Sergeant Sousuke Sagara. Tasked with safeguarding Kaname Chidori, a unique individual known as a 'Whispered' possessing extraordinary knowledge and inventiveness, Sousuke must infiltrate her high school under the guise of a student to shield her from hostile forces. Despite his lack of familiarity with civilian life due to a childhood on the battlefield, Sousuke must navigate the complexities of high school to fulfill his mission. As threats close in, Sousuke realizes that the danger targeting Kaname may be closer than he ever imagined.