Sosuke Sagara, an elite eighteen-year-old sergeant working for the covert counter-terrorist mercenary organization Mithril, receives a perilous undercover assignment. His mission is to protect Kaname Chidori, a spirited Japanese high school student who unknowingly possesses the "Whispered"—advanced, subconscious technological knowledge sought by global terrorist factions. Disguised as a
transfer student at Jindai High School, Sosuke struggles profoundly to adapt to normal civilian life. Having been a child soldier in war-torn regions, his hyper-vigilant military mindset, penchant for carrying unauthorized firearms, and tendency to solve minor social disputes with explosive force lead to continuous comedic and chaotic misunderstandings.Despite their initial friction, a deep bond forms between Sosuke and Kaname as they endure escalating threats. The narrative shifts dramatically when Gauron, a ruthless and sadistic terrorist working for the shadowy antagonist organization Amalgam, targets Kaname. Gauron captures a commercial airliner, prompting Mithril to deploy its advanced humanoid mecha, known as Arm Slaves, piloted by operatives like Melissa Mao and Kurz Weber. Sosuke joins the fray, piloting his custom, highly advanced Arm Slave, the ARX-7 Arbalest. During these violent encounters, Kaname experiences involuntary flashbacks and mathematical transmissions related to her Whispered status, proving her immense value to the enemy.The tension peaks when Gauron infiltrates Jindai High School, forcing Sosuke into a desperate, high-stakes battle to protect Kaname and his classmates. After a brutal showdown, Sosuke seemingly defeats Gauron, but the victory is short-lived. Amalgam’s relentless pursuit forces Sosuke to confront his own traumatic past, the mysterious origins of the Whispered technology, and the terrifying realization that Mithril has been severely compromised by a mysterious mole within their higher ranks.Throughout the escalating conflict, the central emotional core remains the complex dynamic between the emotionally stunted, battle-hardened soldier and the fiercely independent, compassionate schoolgirl. As Sosuke learns to balance his duty to Mithril with his genuine feelings for Kaname, the overarching war against Amalgam expands globally. The conflict introduces heavier
political intrigue, betrayal, and state-of-the-art mecha warfare, leaving Sosuke and Kaname facing an uncertain, perilous future where their survival depends entirely on their trust in one another amidst a world teetering on the brink of catastrophic global war.