The XM2 Reginleif (レギンレイヴ, Reginreivu?) is an experimental third-generation Feldreß from the Federal Republic of Giad. It was designed by Lieutenant Colonel Grethe Wenzel and inspired by the Republic of San Magnolia's M1A4 Juggernaut. It is built for high-mobility attacks as part of a mobile defense strategy.
Reginleif is one of the Valkyrie of Norse Mythology, whose name possibly means "Power-trace" or "Daughter of the Gods". Its designation of XM2 stands for Experimental Model 2.
As the Reginleif was based on the Juggernaut, they share the same general design with a top mounted cannon, two sub-arms for secondary armaments, and a quadrupedal walker system designed for high mobility. The two Feldreß also are used in similar tactics, used for hit-and-run and mobile defense strategies, unlike other slower Feldreß such as the M4A3 Vanagandr. The Reginleif is described as having bone-colored armor, pushing the machine's resemblance to a skeleton knight.
The Reginleif's impressive performances, however, are a double-edged sword. It's very difficult to be controlled by average pilots. Many operators were killed during its early stages of testing, with most Federacy soldiers unable to utilize the full extent of the unit's mobility. Currently, the Reginleif is only used by the members of the Eighty-Sixth Strike Package.
The Reginleif has a similar cockpit configuration to the Juggernaut, with an added auxiliary seat for a single passenger. The cockpit uses a projector system to create a HUD in front of the pilot and has normal displays on both sides of the cockpit's lower back section for engine power and resource management. The cockpit's seal is able to protect Processors from biological and chemical weapons.
The Reginleif usually packs a high-velocity 88 mm smoothbore gun that can fire both APFSDS (Armour Piercing Fin-Stabilized Discarding Sabot) or HEAT (High Explosive Anti-tank) rounds using a double feed system. The cannon can also be switched out for multiple-rocket launcher pads, as used by the Snow Witch, an autocannon like that mounted on the Wehrwolf or the Howitzer artillery guns used by the Archer and Quarrel squadrons. The 88 mm cannon itself can also be modified to the user's preferences. The Gunslinger has an extended barrel to improve accuracy and shell velocity while Cyclops was modified to use a canister shotgun that specialized in firing buckshot rounds. The maximum range of the main gun is approximately 7km.
The secondary armaments of the XM2 include the pair of arm mounts and wire anchors found on the M1A4, with the arm mounts being able to equip either high-frequency blades for close combat or 12.7 mm heavy machine guns. The Sagittarius was shown to be equipped with smoke dischargers to provide cover for the vanguard. The XM2 also had four pile drivers added, one on each leg. The pile drivers are used for close combat to pierce the armor of the Legion and can each be used twenty times. In combat, the pile drivers sometimes become stuck to the Legion and have to be purged.
The XM2 is visibly more armored than the M1A4. Compared to the M1A4's complete lack of safety features for the Processor, the XM2 has significant armor increases that allow it to withstand the machine gun fire of the Ameise. While the Legion has changed the Ameise armament to a 14mm heavy machine gun in order to defeat the armor of the XM2, the improved armor is nonetheless a great improvement in defense against shrapnel.
The XM2 is not suited to operate in high-temperature environment. Its thin armor and cooling system only allow the XM2 to operate in such environments for a few hours. 
The XM2 is also noted to have greater speed and maneuverability compared to the M1A4 in spite of the increased weight from the larger gun and thicker armor, implying that the XM2's propulsion systems have been upgraded. The Reginleif is capable of reaching an off-road cruising speed of over 100 km/h.
- Many Federacy soldiers dislike the Reginleif due the Republic-based design which utterly disregarded the operator's safety.
- The primary gun is inspired from the famous German high velocity 88 mm flak fielded during WW2. However, it is nicknamed "Ratsch Bumm" instead of the original nickname Acht-Acht (8-8 in German), as it is too similar to Asato's pen name.
- The Wehrwolf was altered to use a 30 mm caliber autocannon in the anime, instead of the 40 mm caliber used in the light novel.