Mithril, a covert military organization employing cutting-edge technology to counter terrorist activities, tasks a specialized unit with a delicate assignment. Led by superior officer Melissa Mao, sergeants Sousuke Sagara and Kurz Weber are ordered to secretly safeguard Kaname Chidori—a teenage girl who unknowingly possesses groundbreaking scientific knowledge and is labeled a "Whispered"—from intelligence agencies and other groups seeking to exploit her abilities. While Kurz and Melissa provide remote support, Sousuke enrolls in Kaname's high school as a fellow student to keep a close watch on her. However, his military background and lack of social skills cause significant difficulty in adapting to civilian life. He not only draws unwanted attention but also frequently arouses Kaname's suspicion through his behavior. Despite his sincere efforts to carry out his mission, a terrorist ambush further complicates Sousuke's duties. Upon identifying the ruthless mastermind behind the attack, Sousuke disregards his orders to guarantee Kaname's safety.