"I am Legion, for we are many." ― Mark 5:9
The Legion (レギオン, Region?) is a collective, self-sustaining, AI army that comes from the remains of the Giadian Empire. The AI system was invented by the United Kingdom of Roa Gracia, while the mechanical bodies use technology derived from the Alliance of Wald. Using the neighboring countries' innovation, the old Empire produced the Legion as a perfect drone army before their downfall.
The Legion is capable of scanning and replicating a brain's state postmortem and incorporating it into their processing capabilities. The Legion required the assimilation of the deceased to replace their deteriorating central processors, which are set to expire after 50,000 hours or around six years of usage time.
The Legion was created by Major Zelene Birkenbaum using the Mariana Model AI developed by Viktor Idinarohk. The Legion was first deployed by the Empire in the RY 358, where they were used to invade neighboring countries. During the same year, a revolution broke out against the imperial faction. The revolutionaries won out against the imperials, eventually establishing the Federal Republic of Giad.
The victory of the revolutionaries did not lead to peace, however. Just as the imperial faction was about to be completely annihilated, the high ranking members assimilated themselves as Shepherds and gave one final order to the Legion, "Destroy the enemy." This caused the Legion to become an uncontrollable army, whose purpose was to seek humanity's extinction.
The Legion managed to encircle many nations, locking them out of communications and slowly conquering their territories.
- Chapter 3
Through the information obtained by interrogating Zelene, who had by then been assimilated, the method to the Legion's deactivation was made clear. The method required a member of the Giadian Royal Family to transmit a shutdown code in an Imperial fortress deep within Legion territory. Only Vika and Shin are privy to this information, and only Shin knows that it is possible to do so through Frederica Rosenfort.
The Legion, typically, does not operate during nighttime. They fundamentally operate during the daytime to harness solar energy and generate electricity to maintain their vitality when their energy packs have been exhausted. Nighttime operations, when they are not able to recharge through solar energy, exposed them to the risk of running out of power mid-combat. As a result, the Legion generally avoid engagements during nighttime unless a high possibility to cripple the enemy is calculated.
The Legion is forbidden in its philosophy and programming to field certain types of weapons, as the Legion was intended for subjugation instead of extermination. Bioweapons and units that are indistinguishable from civilians are forbidden due to this philosophy. Combat aircraft and bombers are also forbidden due to the biases of Major Birkenbaum.
As the Legion is built to fill the roles of non-commissioned officers and common soldiers, a safety measure is applied to them; If the Legion does not received new orders for a specific period of time, they are to request new orders from a member of their assigned leadership. And if no such a person is available, then the Legion will seek out a successor whom they deem fit to command them.
All Legion processors were originally set to have an expiration time of 50,000 hours for every version update. This lifespan was originally unchangeable, intended to be a failsafe against the Legion should they go berserk. With the fall of the Empire, the Legion required a way to update or replace their central processors, resulting in them assimilating the brains of the dead. This limitation no longer applies to the Legion.
Finally, all units of the Legion can be shutdown as a final safety measure. To do so, the shutdown code must be transmitted from a specific imperial fortress which is, at the present, located deep inside Legion territory. However, one essential condition is that a person who transmit the code must has command right over an entire Legion forces; Only people, qualified to receive command right, are the descendants of the Giadian Imperial bloodline. 
- White Sheep: The Legion which had not yet replaced their central processors. They are extinct by SY 2150, since the lifespan of their processors would've run out if they've not been replaced.
- Black Sheep: The Legion that had adopted the decayed brain structure of dead humans, capable of limited human intelligence.
- Shepherd: The Legion that had adopted the un-decayed brain structure of living or recently dead humans, capable of full human intelligence and leadership.
- Sheepdog: Mass-produced intelligent Legion created by adopting fresh human brains with memory portion removed. They are capable of human intelligence, but not affected by human emotions.
The Legion comes in various models specialized for different tasks.
- Ameise: Scout Type. Their main feature is their enhanced sensors and high mobility. Equipped with dual 7.62mm anti-personnel machine guns, but some models are upgraded with 14mm anti-material heavy machine guns. One of the most common legion units on the battlefield.
Main Article: Ameise
- Grauwolf: Dragoon Type. Equipped with high-frequency blades and 76mm guided anti-tank rockets. Despite being larger than the Ameise, they are far more mobile, being fast enough to run on vertical walls, but at the cost of having next to no armor, and can be disabled even by a Juggernaut's 12.7mm machine guns.
Main Article: Grauwolf
- Löwe: Tank Type. This unit is equipped with heavy armor on the front and sides, a 120 mm main cannon and a 12.7 mm coaxial machine gun. Much like conventional tanks, their top, bottom and rear armor are weaker and can be penetrated by the Juggernaut's 57mm cannon.
Main Article: Löwe
- Dinosauria: Heavy Tank Type, weighing 100 tons. Strongest of the regular units. armed with a 155 mm cannon turret, a 75 mm secondary coaxial cannon, two 12.7 mm heavy machine guns mounted on the turret, and the capability of employing liquid micromachine "arms". A second variant exists that replaces the 75mm cannon with a flamethrower and one of the 12.7mm machine guns with a smaller 7.62mm general purpose machine gun.
Main Article: Dinosauria
- Skorpion: Long-Range Gunner Type. A heavily-armed Legion that provides artillery support with a 155 mm howitzer or a multiple rocket system from far behind the battlefield.
Main Article: Skorpion
- Stier: Anti-Tank Artillery Type. As it possesses high-firepower at the cost of low-mobility and armor, its only viable deployment is in ambushes.
- Self-Propelled Mine: Antipersonnel Type. This Legion unit “clings” to humans or human-made weapon systems before self-destructing. Its tactics are simple though often inefficient. It is roughly the same size as a human and can therefore be equipped with antipersonnel rifles.
Main Article: Self-Propelled Mine
- Stachelschwein: Anti-air Type. Immediately after the war began, they were scattered throughout the combat zone, completely rendering aircraft unusable. They're armed with rapid firing autocannons and can easily shred aircraft apart and can also function as mobile C-RAM units, as they're capable of shooting down the guided artillery shells fired by the Republic's interception cannons.
- Morpho: Railgun Type. Equipped with a railgun capable of long-range accurate bombardment of up to 400 km. It is also equipped with multi-barrel electromagnetic Vulcan cannons used as CIWS (Close-in-weapon-system) to defend against close range enemies and incoming missiles. The massive weight of 1,400 tons makes its movement troublesome, but the uses of old abandoned railroad tracks allows it to overcome this weakness.
Main Article: Morpho
- Noctiluca: Electromagnetic Gunboat Type. Serves a similar purpose to the Morpho in terms of long-range bombardment using railguns. As an aquatic vessel, the weight of the unit is not as detrimental to its movement.
Main Article: Noctiluca
- Phönix: High-Mobility Type. Capable of exceptional stealth and mobility, it specializes in high speed combat along with utilizing its two chain blades. It also uses liquid armor and is proven to be capable of transforming parts of its armor into projectiles.
Main Article: Phönix
- Zentaur: Catapult Type. It is used to deploy Legion units such as the Phönix and Skorpion deep into enemy lines in a paratrooper-like fashion.
Main Article: Zentaur
- Biene: Fire Extension Type. They are small, spider-shaped laser shooting Legion units were used by the Legion in their defense of the Charité Underground Labyrinth. While powerful enough to penetrate the XM2 Reginleif's hull, they are extremely power-hungry and are thus connected to the Admiral unit and serve as its point defense weapons.
- Edelfalter: Generator extension Type. A palm-sized butterfly legion with solar powered panel wings usually used to assist in transferring power from the Admiral to other Legion units. They are also used by the Morpho to recharge after firing the railgun.
- Eintagsfliege: Electronic Disruption Type. These mayfly-shaped tiny Legion units spread throughout the skies. They jam communications, making long distance communication impossible by absorbing, refracting and disrupting all electromagnetic waves. It has the shape and size of a butterfly with a body length of around 10 cm and weighs about 2 grams. It is deployed in the battlefield as a vanguard to confuse enemy radars as well as flying into planes' air intakes to disable aircraft engines.
Main Article: Eintagsfliege
- Rabe: AWACS & ELINT type, a huge bird shaped Legion with a 122 meter wingspan that flies at an altitude of 20,000m or roughly 65,000ft. It is the commander unit for the Eintagsfliege swarms, and has the role of integrating and analyzing the communication between the legions.
Main Article: Rabe
- Admiral: Energy Production Type. They are large, butterfly shaped Legion units that typically produce energy packs via solar energy with solar panel wings, but there have been some confirmed to use geothermal energy, or a flawed, experimental form of nuclear fusion that, while highly efficient, prevents smaller Legion units from operating around it as it leaks large amount of radiation that can potentially damage their electronics.
- Weisel: Auto-Production Type. A massive city-block sized Legion meant for the production of Legion vehicles.
- Tausendfüßler: Recovery Transport Type. A giant steel centipede which acts as the Legion's scavengers and neural assimilators.
While the Legion is indifferent towards humans in general, there are a number of humans who are deemed to carry strategic significance by the Legion. When they discover such people, the Legion will give them a code name and designate them as a high-priority target for capturing or assimilating. So far, people who are designated as a High-priority target include:
- Shinei Nouzen, Code Name: Báleygr, for his unusual ability to pinpoint Legion locations and a potential successor to receive to right to command the Legion.
- Viktor Idinarohk, Code Name: Hveðrungr, for developing the drone-piloting system, the Sirins.
- Henrietta von Penrose, Code Name: Minerva, presumably for her ability as a researcher.