The X series robots are bipedal panzer, co-developed by the Police Department and Defense Agency, and conducted by General Sugawara of the ground army. The cockpit contains a nerve transplant device to connect the pilot's brain with the operating system of the robot for enhanced synchronization. The firepower from a M249 light machine gun and L16 81mm mortar and the "Muramasa Copies" wielded on their right arms for sealing the Persona ability from Persona users temporarily suggest the purposes of development of these machines are far beyond the nominal riot control.
When the player's party hacks into the computer of the laboratory of New World Order in Kei Nanjo's route, they will learn the existence of the X series project and involvement of the army.
The apparent differences with the Knights of the Holy Lance is the lack of flight capability but able to travel underwater. The Knights use mostly magical-based abilities, but the repertoire of the X series is entirely physical.
Although the X series robots are co-developed by the ground army, in the opening movie, the department name printed on the armor is "Maritime SDF" (海上自衛隊, Kaijō Jieitai)?. However, this is possibly because they are operating on Nichirinmaru, the restructured cruise ship used by NWO as their maritime headquarters.
The origin of the name "X" is never explained, but this coincides with the symbol "X" for "crime/wrongness" in Japanese culture which is heavily used by the game developers to abbreviate the title of Eternal Punishment ("P2X" as in the official website of Japanese PSP remake).
Since the battle interface has changed in the PSP version, the Persona-sealed status is shown given the name "Wicked Blade" (妖刀, Yōtō)? which is a well-known epithet of the blades forged by the bladesmith Muramasa Sengo.