Sousuke Sagara, an elite, socially inept 17-year-old mercenary for the anti-terrorist organization Mithril, is assigned an undercover protection detail at Jindai High School. His target: Kaname Chidori, a hot-headed schoolgirl who may secretly possess world-altering Black Technology.
Sousuke's complete inability to function in civilian society results in utter chaos as he uses military-grade tactics to handle minor high school inconveniences. Meanwhile, the ruthless terrorist Gauron begins making his move to capture Kaname.
The high school field trip to Okinawa goes violently off the rails when the plane is hijacked by Gauron's heavily armed forces. Sousuke is forced to drop his cover and rely on his brutal combat instincts to keep Kaname alive.
Trapped in a secret facility in North Korea, Kaname's latent "Whispered" abilities begin to awaken under intense psychological pressure. Sousuke coordinates a desperate, high-risk rescue operation to break her out of the heavily guarded compound.
Mithril launches a massive counter-attack. Pushed to the absolute brink by Gauron's advanced Arm Slave, Sousuke is forced to pilot the experimental ARX-7 Arbalest. Guided by Kaname's Whispered intuition, he activates the reality-defying Lambda Driver.
The dust settles after the brutal battle. Sousuke and Kaname navigate the awkward, terrifying aftermath of their escape, forging a deep, unspoken bond built on the trauma they just survived together.
Kaname returns to her normal life at Jindai High, but the reality of Sousuke's bloody profession lingers between them. An emotional breather that solidifies their bizarre, deeply protective dynamic.
A classic FMP! comedic detour. Shirou needs a fake girlfriend to impress his visiting former flame, dragging Sousuke, Kurz, and Melissa Mao into a ridiculously over-engineered, disastrously executed charade.
Melissa Mao's fiercely independent past is explored when her estranged, aristocratic ex-fiancé tracks her down. Kurz and Sousuke get dragged into a chaotic, alcohol-fueled bar fight to protect their commanding officer's honor.
Absolute comedy gold. Sousuke and Kaname visit the JSDF Narashino base for a festival, only for Sousuke to ignite a massive, violently competitive rivalry between the military platoons over a trivial contest.
Kaname takes shelter in a Mithril safe house when a rogue terrorist faction known as A21 begins operating in Tokyo. The tension ramps up as Sousuke realizes the safe house has been completely compromised.
Sousuke and Kaname are forced on the run through the neon streets of Tokyo, engaging in brutal, close-quarters urban combat against A21's elite assassins who are determined to capture the Whispered.
A21 unleashes their ultimate weapon: the Behemoth, a colossal, impossibly massive Arm Slave that defies the laws of physics using a Lambda Driver. The sheer scale of the machine leaves Mithril's standard forces completely outgunned.
Sousuke drops into Tokyo in the Arbalest for a desperate, David-vs-Goliath clash against the Behemoth. With the city crumbling around them, Kaname uses her Whispered knowledge to find the massive machine's single, fatal design flaw.
Sousuke, Kurz, and Mao are deployed to the war-torn deserts of Helmajistan. Sousuke is forced to confront the ghosts of his past as a child soldier when they cross paths with his old guerrilla mentor, who is now leading a resistance force.
The mission goes catastrophically wrong. Separated, out of ammo, and stranded in the blistering desert, the Mithril pilots are relentlessly hunted by an enemy ace in a customized Arm Slave.
Pushed to his absolute physical and mental limits, Sousuke executes a brutal, brilliantly tactical ambush in the desert canyons to eliminate the enemy ace, proving why he is Mithril's most lethal specialist.
Kaname is invited aboard the Tuatha de Danaan, Mithril's hyper-advanced, Whispered-designed submarine, to attend a celebration. She bonds with Captain Teletha "Tessa" Testarossa, sparking a quiet rivalry over Sousuke.
The celebration is violently interrupted when the seemingly dead Gauron infiltrates the submarine. Utilizing a terrifyingly precise mutiny, he systematically takes control of the most powerful warship on the planet.
With Gauron in control of the ship's AI, Tessa and Kaname are forced to navigate the claustrophobic, lockdown-sealed corridors of the submarine. Gauron's sadistic psychological warfare begins to tear the crew apart.
Sousuke and Kurz launch a desperate, two-man guerrilla campaign inside their own submarine to retake the engineering decks. The tension skyrockets as Gauron arms the Danaan's massive cruise missiles.
Kaname and Tessa link their Whispered minds to directly interface with the submarine's core systems, engaging in a high-speed, digital hacking war against Gauron's overrides to prevent a global catastrophe.
Sousuke finally corners Gauron in the hanger bay. The two rivals deploy their Arm Slaves inside the confined, highly explosive belly of the submarine for a brutal, metallic deathmatch.
The explosive finale. Sousuke pushes the Arbalest's Lambda Driver to its absolute peak to annihilate Gauron's Venom. The crew successfully retakes the Danaan, and Sousuke returns to his bizarre, peaceful high school life with Kaname.