Irvine Lester operates an Armored Trooper repair shop with his younger sister Donna, both struggling to make ends meet in their impoverished surroundings. He longs to escape to a better world with her. To fund this goal, he leads a double life, secretly competing in illegal AT gambling matches under the masked alias "The Dark." As part of an arrangement with promoter Ishruna, he intentionally loses rigged matches against a fighter named Pagan.

A former AT pilot for the Gilgamesh Confederation, Irvine possesses a military background and exceptional piloting skills. When these abilities become known to others in the battling circuit, they demand he compete in legitimate matches. The situation escalates after Pagan uncovers the deception behind the fixed fights. Pagan's intense rage drives him to target not only Irvine but also his civilian life and his sister Donna, pulling them into a dangerous conflict. Throughout, Irvine remains motivated by his protective instincts toward Donna and his determination to secure a better future for them both.