The original universe of the Armored Core franchise. In it, Mankind was forced underground due to the aftermath of the Great Destruction, a cataclysmic war. In the underground era, Corporations emerged to control the world and their battles lead to the rise of the Muscle Tracer and eventually the titular Armored Core. However, it was revealed that all of these events were the machinations of an AI known as Hustler One. With its destruction by Leos Klein, a new Government emerged to reign in both the Corporations and Ravens.
Decades later, it was discovered that one Corporation, Murakumo Millennium was planning on Terraforming Mars. These plans were enacted by their successor, Zio Matrix causing mass migration to the Red Planet. However, the war between Zio and Emeraude continued unabated and the Government sent LCC to keep them in check. Using their Special Forces unit, the Freightners, the LCC gained the upper hand until their leader betrayed them and tried to destroy Mars with Phobos, an ancient alien weapon.