Mithril, a clandestine military organization equipped with advanced technology to thwart terrorist activities, deploys a specialized team for a critical mission. Under the leadership of commanding officer Melissa Mao, sergeants Sousuke Sagara and Kurz Weber are tasked with the covert protection of Kaname Chidori—a teenager who unknowingly possesses groundbreaking scientific insights and is identified as a "Whispered"—shielding her from intelligence entities and other groups seeking her capabilities.
While Kurz and Melissa provide remote support, Sousuke joins Kaname's high school posing as a fellow student to keep a close watch on her. His military background and lack of social finesse, however, make assimilating into civilian life challenging. His behavior not only draws unwanted attention but also raises Kaname's suspicions about him.
In spite of his genuine efforts to execute his mission, a terrorist strike adds complexity to Sousuke's assignment. Identifying the cruel strategist behind the attack, Sousuke disregards his original orders to guarantee Kaname's protection.