Zone of the Enders: 2173 Testament (Z.O.E: The Fist of Mars in Europe and North America) features a different concept of robot simulation. Instead of the traditional action/shooter-type gameplay in Zone of the Enders and The 2nd Runner, 2173 Testament involves more of a strategy/RPG-type gameplay, giving players a new experience.

The game features all new characters and Orbital Frame models not found in either of the PlayStation 2 games, and, as its name implies, takes place after the events of Zone of the Enders and before The 2nd Runner.