In the world of Xenogears, Gears are used in major wars or combat. These are basically giant mechanical robots that are piloted by a single person. There are all sorts of Gears. Civilian Gears are Gears that does not have the abilities to fight. Instead, these Gears are mainly used for travelling or excavating the ruins. Military Gears are used mainly for fighting (duh!) and they cause massive damage. Military Gears are much more complicated to pilot than the civilan Gears. Most of the pilots have to go through a certain form of training before even knowing how to move the Gears. When piloting Gears, the strength of the Gear depends on the mental strength of the pilot. This is especially so in Omnigears, which will be explained later. Pilots can use a certain drug called "Drive" to help them perform better when piloting the Gears. However, this drug has a few side effects such as causing the pilot to lose all of his/her personality traits. Also, an overdose of Drive may kill the pilot.

Among the many Gears in the world of Xenogears, there is a special kind of group of Gears called the Omnigears. These Gears are extremely powerful and will destroy most other Gears in seconds. However, in order to obtain such Gears, a process must be carried out. First of all, Anima Relics must be found. These are relics created by the ancient Zeboim Civilization. When an Anima Relic is found, a normal Gear must be lined up with the Anima Relic in order to create an Omnigear. After the Omnigear is created, it would then call out to its owner if its owner were nearby. Hence, the Omnigear "selects" its own owner. The owner of the Omnigear would most likely be the owner of the Gear lined up with the Anima Relic. However, this is not always so. A person would not be able to pilot an Omnigear if the Omnigear does not recognize the person as its owner. In the Omnigear itself, there is no control stick or other buttons to control the Omnigear. Instead, the pilot must communicate mentally with the Omnigear in order to control and maneuver it. Only when there is full mental synchronization between the pilot and the Omnigear, will the Omnigear be exceptionally powerful. Hence, the power of the Omnigear sometimes hinges on the mental strength of the pilot.