You step into this era of war as a single Gunbat. You can fight with your machine customized as you like. You are free to accept requests. You are free to be hired by corporations. You are free to cooperate with AMSAS or live as an independent mercenary. But no matter which path you choose, you will eventually encounter them. —The five ghosts who changed Martian history.

Atlas Palecia, a cluster of emerging cities in the Martian southern hemisphere. It was the front line of resource development and Mars' largest battlefield where corporations, the military, environmental armed organizations, and Gunbats (mercenaries) from all over the world gathered. The B-Ghouk member corporation Valendrance Corp seeks resources, the environmental armed organization CoN takes up arms to stop development, and the AMSAS Frontier Expeditionary Battalion intervenes under the guise of maintaining order. Everyone fought for their own justice and profit, and the endless proxy war was intensifying. But that balance collapses due to a single incident. A total war over the massive oil mining base, Armline. Five CH units suddenly appeared on that battlefield. They struck the Corporate forces, they struck AMSAS, and they struck CoN. Ignoring even the concept of friend or foe, they rewrote the battlefield itself with overwhelming combat power, finally bringing Armline to destruction. It is the Armline Incident, which remains in Martian history. Following this incident, one name became known throughout Mars. The Spriggans. Oberon 1. Undine 2. Gremlin 3. Pixie 4. Cait Sith 5. Identity unknown. Purpose unknown. Affiliation unknown. A mysterious armed group that repels armies, sinks fleets, and dominates the battlefield with only a few members. Are they terrorists, heroes, or beings with some other purpose? No one knows the answer. Eventually, every faction on Mars begins to pursue them. Some to subjugate them. Some to utilize them. And some to reach the "truth" that lies beyond them. This is the beginning of the "Spriggan Incident," which would later greatly shake Martian history.

Atlas Palecia: A cluster of emerging cities built inside a giant crater in the Martian southern hemisphere. It underwent rapid development triggered by the discovery of large-scale mineral resources sleeping underground, becoming a center for mining, refining, and logistics. Corporations, the military, environmental armed groups, and mercenaries fight over its vast interests, leading it to be called "Mars' largest powder keg."

Valendrance Corp: A republican land development corporate community belonging to the B-Ghouk Corporate Alliance. A giant corporation leading urban and resource development in Atlas Palecia, it operates numerous private armies and Gunbats to protect its vast interests. Among the development-oriented companies in the alliance, it possesses particularly strong military power and political influence.

CoN: An environmental armed organization advocating for the preservation of the Martian natural environment and underground primordial microbial ecosystems. They engage in radical resistance activities, including sabotage and the use of force, against the unregulated urban and resource development by corporations, and are feared as a terrorist organization by various factions. On the other hand, many sympathize with their ideology.

AMSAS Frontier Expeditionary Battalion: An expeditionary force dispatched to Atlas Palecia by the AMSAS Central Administrative Committee. While active under the pretext of maintaining public order in frontier regions and protecting AMSAS interests, they actually conduct military interventions against corporate forces and armed groups. It is the region's largest regular military force, possessing CH units, land combat units, and fleet assets.

Spriggans: A mysterious elite armed group. They are shrouded in mystery. Their actions lack consistency in terms of factional interests, and they are sometimes regarded as neutral, indiscriminate terrorists.