The game is set on a fictional planet called Alter 8, where players take on the role of Junkmetal pilots, mercenaries who operate customized robots to explore, fight, and survive. It has a unique and complex backstory, involving a secret plan by POF (i.e. Planet of Fortune), a huge private company, to terraform and colonize Alter 8, the emergence of a mysterious threat called GHOUL, and the eventual collapse of the planet.

JunkMetal is a MMOFPSRPG developed by Metro and published by Enix in 2003. It features a high degree of customization, allowing players to mix and match various parts and weapons for their robots, as well as different operating systems and software. Also, it emphasizes PvP (player versus player) combat, where players can join one of two rival factions, POF or Infinity, or remain as freelancers.