The Gaia is a transformable unit specialized in high-mobility ground combat which can transform into a quadruped mode for increased speed. Designed to be able to go toe-to-toe against ZAFT's TMF/A-802 BuCUE, its speed in quadruped mode is equal to that of the BuCUE in spite of the fact that it lacks the latter's leg-mounted tank treads. While the Gaia is designed to operate equally well in space as well as on Earth, it is incapable of atmospheric aerial combat. However, the array of thrusters mounted in the "wings" on its back enable it to make fairly high thruster-assisted jumps, enabling it to attack low-flying aerial targets.
The suit is lightly armed, as its mobility is its primary advantage. It is equipped with CIWS guns for anti-MS/missile interceptions as well as a long-range beam rifle and two beam sabers. In quadruped mode, it is also able to use a pair of powerful beam cannons as well as a pair of wing-mounted beam blades.
Since the Gaia cannot use its beam sabers in quadruped mode, it is instead armed with a pair of beam blades mounted on long wings, the back of which is lined with thrusters that enable it to perform a high-speed charge against an enemy unit and slice it in two. Though insufficient to allow true flight, these wings also serve as control surfaces in thruster-assisted jumps or in zero-gravity.
The Gaia is equipped with Phase-Shift Armor. Improvements in the technology in recent years mean that it is far more energy-efficient than it previously was, causing a much-reduced drain on the battery.
When the First Junius War ended, more than half of the Earth Alliance's military strength had been annihilated. In the following years, the Atlantic Federation began to work towards rebuilding its lost military might, and they contract this out to two of the Alliance's largest weapons manufacturers - National Defense Industries (formerly known as the Azrael Conglomerate), and Adukarv Mechano-Industries. Over the intervening years, a number of mobile suits are developed, beginning with the GAT-01A2 Dagger and GAT-04 Windam. In addition to this, the two manufacturers begin work on more powerful prototype units. After producing the TSX-MA24F Chaosin conjunction with rival Adukarv, NDI chose to turn its attention to variable mobile suits, and in CE 74 began development on two prototypes: The aquatic mobile suit GAT-X731 Abyss Gundam, and the high-mobility ground combat GAT-X388 Gaia Gundam.
The Gaia Gundam was designed specifically to go head-to-head with ZAFT's TMF/A-802 BuCUE, and as such is designed as a lightweight, high-mobility assault mobile suit specializing in ground combat. In mobile suit mode, the Gaia's armament is rudimentary, consisting of a long-range beam rifle and a pair of beam sabers, as well as a pair of CIWS mounted in its head. Its primary advantage is its high mobility, thanks to an array of thrusters built into a pair of wings on its back. The wings themselves do not generate sufficient thrust to allow the Gaia full-fledged flight capability, however it does enable it to launch into fairly high-altitude powered jumps, similarly to the original Strike Gundam's Aile Striker. The Gaia is able to transform into a quadruped mobile armor mode patterned on the BuCUE, albeit lacking the latter's leg-mounted threads. In spite of this, its running speed in quadruped mode is nearly equal to the BuCUE's top speed. In quadruped mode, it is able to use the beam rifle as a fixed beam gun, supplemented by a pair of powerful beam cannons mounted over its shoulders. In lieu of its head-mounted CIWS, the Gaia's cowl, which forms the head of its quadruped mode, mounts two pairs of CIWS of its own. The Gaia's deadliest weapon is a pair of long beam blades, each one mounted along the leading edge of its wings, allowing it to make high-speed, close-quarters attacks.
The Gaia is assigned to Extended Stella Loussier and initially based on the stealth battleship Nana Buluku, from which it is first deployed on February 14, CE 75, against ZAFT's new warship Minerva , during an operation carried out by rogue extremist Coordinators to drop the remains of Junius Seven onto Earth. Misunderstanding the situation, Stella and her teammates attack both the terrorists and the Minerva's mobile suits, which were attempting to both stop the colony from falling and protect the multinational Memorial Delegation which was at the site for the anniversary of the Bloody Valentine Tragedy.
The Gaia was later transferred to Earth and operated from the Atlantic Federation carrier John Paul Jones. During its time on Earth, it again battled against the Minerva two times. During the second battle, Stella fought against Heine Westenfluss and his ZGMF-2000 GOUF Ignited, which she is able to defeat. A short time later, Stella launched a solo sortie against orders at the Lodonia laboratory facility. There, the Gaia was disabled by the Saviour and Impulse Gundams, and Stella was captured by the Minerva along with the Gaia. The Gaia is subsequently transported to the PLANTs and dismantled in order to analyze its capabilities.