In the year 24XX, the metropolis known as Aegis 09, was faced with a massive energy crisis. The city had begun to take in too much energy than its Force Metal Generators could produce, and as a result, could face a catastrophic power failure. In desperation, the city's scientists started to experiment, in an attempt to create an artificially more powerful variety of Force Metal. Through many errors, they seemingly created the perfect Force Metal that was dubbed "Crimson Nova". While it seemingly had more power than normal, the side effects were immediately noticed. Machines began to malfunction, reploids enhanced by the Force Metal began to go haywire and attack anyone around them, and the Crimson Nova metal started to corrupt the city's systems.

Aegis 09 had traded one crisis for another, and as a result of reckless experimentation, more than half of the city has been quarantined. Special forces units comprised of volunteers and soldiers are deployed on a daily basis to combat the constant threat of crimson reploids, and scientists are working around the clock to find a way to stop Crimson Nova. One such unit of is about to take a routine patrol through the quarantine zone, a patrol that would become a battle for survival.