Gear was a machine or robot used in major war or combat in the world of Xenogears. This basically a giant mechanical robot that are piloted by single person. There were many kind of gear in Xenogears world. Civilian gears which was used to travelling or excavating the ruins. but they don't have the ability for combat. Second the military gears, were used to fighting, and they could do a massive destruction. Military gears are more complicated than civilian gears. The pilot must take special training from the military first.

There were special kind of gears among the military gears the gears were called "The Omnigears". These gears are extremely powerful and could destroy the standart military gears in second!. These Omnigears depend on the mental power ability of the pilot, and the pilot must the owner of the gear anyone could'nt riding them. The omnigears were result of the transformation from standart military/fighting gears by using the anima relic which was created by Zeboim civilization.