Armored Core: Project Phantasma follows the general storyline of Armored Core. The player is a mercenary Raven who pilots a large mech (or Armored Core).
Project Phantasma allows the player the option of importing their original Armored Core save file, which allowed the player to carry over several AC parts that would not otherwise be available in the game.
Additionally, Project Phantasma introduced the Arena into the Armored Core mythos. Here the player can pit their AC against several dozen opponents, earning cash and unlocking more parts for their mech.