The genuine sequel to the original Armored Core. Thrown into the world of AC mechs, you must complete the objectives set for you by a range of different companies, each with a hefty pay packet attached. If the mission is completed, the money goes towards upgrades and repairs to your mech. The collection of items to upgrade your mech is fully stocked with weapons, defense systems, rocket packs and guidance systems to increase accuracy and speed. Certain missions require a particular upgrade for the mission to be completed correctly, so spending the cash wisely is important to your career. Once your mech is ready for battle, you can also take on a friend in arena mode, where one-on-one battles rage on for as long as you wish in huge outdoor areas.

Sixty-seven years after the events of the Subterranean Era in prior games, Earth's second largest corporation, Zio Matrix, acquires plans for a research project on Mars, dating back before the Great Destruction. Using these plans, Zio sends a research team to Mars to begin the Terraforming Project, which causes the Martian surface and atmosphere to approximate that of Earth. Other corporations learn of the project and quickly follow Zio Matrix, bringing with them the competitive environment that existed on Earth, and the employ of the mercenaries of Nerves Concord. As the three companies' war comes to a close, the most powerful, Zio Matrix, attempts a coup against the government, which has regained control through its elite mercenary team, The Frighteners, led by Leos Klein. But in the chaos that ensues, the Frighteners turn on the government, assassinate the new leader of the LCC, and take control of powerful Disorder technology. The player character is tasked with confronting them and saving the human populace of Mars.