Zearth is the robot assigned to the contracted pilots, in Bokurano. It is 500 meters tall, making mechas, shown in other series, seem ridiculously minuscule in comparison; for example, the Mazinger Z(18 meters), Shin Getter One(55 meters), and Yuusha Reideen(52 meters). Originally, Zearth was revealed to be unnamed, when its' pilots inquired about it, to Coemushi. Later, they mutually decide to name it "Z-Earth", because it's being used to protect the Earth. It is a humanoid robot, equipped with lasers, which are strong enough to tear apart an entire mountain but not strong enough to penetrate to armor of other robots, and very thick armor, to the point that no man-made tool is able to even scratch it. Inside, a spherical object encases the pilots of Zearth, with a chair for each pilot, reflecting his or her preferences. On its' face, there are several lights, which reflects the amount of living pilots that it has; one dims down for every pilot that is deceased. Additionally, it has very long arms and legs, which prove advantageous at various instances; and when they're not, part of the appendages may be severed. Coemushi hides Zearth in the ocean, when it is not used in battle.
Note: In the Bokurano manga, after Maki names it, she explains that the name is really "The Earth", but shortened to "Zearth" for simplicity.