Pilot: Guest Manufacturer: Federation Forces 3rd Development Division Affiliation: Federation Forces A giant humanoid combat robot characterized by its red armor. Equipped with heavy weaponry across its entire body, it is specialized for anti-group combat. It can wipe out enemies by locking onto multiple targets and firing all weapons simultaneously. It also excels in close-quarters combat, possessing several times the horsepower of mass-produced units. Since it was originally designed to operate alongside its brother unit, Black Zeta, it can be at a disadvantage in terms of movement speed when facing Black Zeta as an enemy.

Full Name: Kotone Ibuki Gender: Female Affiliation: Federation Forces Appearance: Short black hair The operator for Guren Zeta. Serious to a fault, though she occasionally makes somewhat airheaded remarks. She supports Guren Zeta and its pilot, Guest, by operating from a remote location. She harbors secret feelings for Guest and is completely devoted to them. While she curses Carlos for stealing Black Zeta and calls him a traitor, she secretly suspects there might be more to the story.

Full Name: Klein Grail Gender: Male Appearance: Blonde hair, glasses, suit Affiliation: Federation Forces Supreme Commander of the Federation Forces. A brilliant commander who always makes calm judgments. He prefers rational thinking but has a radical side. He strictly orders Guest not to hesitate when facing Black Zeta. Born into a family of high-ranking government officials, he was raised with the belief that overwhelming power and status are necessary to end conflict. ■ Hidden Side Klein has a hidden side that he keeps concealed. He will not reveal this unless Guest and Carlos reconcile or one of them dies. He plans to use Guren Zeta and its pilot, Guest, as pawns to seize control of the World Government once the war with the Rebels is over. His goal is to create true peace by ruling the world himself. He will eliminate anyone without hesitation to achieve this; he even disposed of Carlos's younger sister when she learned the truth. He has already prepared countermeasures in case Guren Zeta and Black Zeta turn against him.

Pilot: Carlos Rain Manufacturer: Federation Forces 3rd Development Division Affiliation: Rebel Army A giant humanoid combat robot with black armor. The brother unit to Guren Zeta, currently operated by the defector Carlos as a Rebel machine. It excels in high-speed movement using the verniers on its back and close-quarters combat with swords equipped on its limbs. It closes the distance instantly to strike at vital points. Since it was originally intended to be paired with Guren Zeta, it is inferior in terms of raw firepower.

Full Name: Carlos Rain Gender: Male Appearance: Brown hair, scar on cheek Affiliation: Rebel Army The pilot of Black Zeta. A former colleague of Guest and Kotone, he betrayed the Federation and stole Black Zeta. He is now conducting raids on Federation bases. Originally a straightforward and friendly person, he now tries to be a cold-blooded warrior. However, he still dislikes methods that involve civilians. While feeling guilty toward Guest and Kotone, he throws himself into the fight against the Federation. He occasionally suffers from his lingering affection for his former comrades. ■ Reason for Betrayal Carlos's younger sister died a sudden, mysterious death. In the process of investigating, he discovered that the Zeta series was 'scheduled to be used for political infighting within the government after the war.' His sister's death was a silencing ordered by Klein. Driven by rage against the Federation, Carlos decided to steal Black Zeta. He agonizes over whether he should tell the truth to Guest, who pilots Guren Zeta. Whether he is treated as a traitor or fights alongside Guest against the Federation's darkness depends on Guest's choices.

Pilot: Klein Grail Manufacturer/Affiliation: Grail Faction A giant humanoid robot with gold armor. A machine that Klein had the Grail family and its supporters build in total secrecy. It is a brother unit to Guren Zeta and Black Zeta, but almost no one in the Federation or the government knows of its existence. It is the machine Klein intends to pilot if the Zeta series pilots betray him, and its performance is tuned for both long-range and close-quarters combat. While it seems invincible, a slight chance of victory exists if Guren Zeta and Black Zeta coordinate their attacks. Essentially the final boss, appearing only when Guest and Carlos reconcile or when Guest turns against Klein.