In the last mission, you get to face an old enemy from the original Armored Core series, albeit in different form: Nine-Ball. However, it was later revealed that 'Nine-Ball' was a prototype Pulverizer, shown in Last Raven. In the Japanese version of Nexus, the name read as '???'. Where Nine Ball came from was either from error, or because the translators thought it would be enticing to feature the old enemy. Despite the errors, this enemy does share similarities to Nine Ball, such as the use of weaponry like the grenade launcher, missiles, and an energy pulse gun, as well as the signature red armor color.
The game is broken down into two discs, EVOLUTION and REVOLUTION. The EVOLUTION disc features all new content in which the story of Armored Core: Nexus is played out. Much like Armored Core 2: Another Age most of the game's arena battles are played out in story-based missions, however a "Free Arena" is unlockable upon completion of the Evolution game's storyline. The REVOLUTION disc takes a look back at previous Armored Core titles, primarily the PlayStation era titles; Armored Core, Project Phantasma and Master of Arena. Completing missions in REVOLUTION unlock extra parts for a player's AC which are based on parts that appeared in previous AC games, including custom parts featured on the AC of Project Phantasma's main antagonist, Stinger, now available to the player for the first time ever.