With the arrival of the Arche-Ymirus mechs on the battlefield, humanity gradually gained the upper hand. Having conquered the environment around them, they began to sink into internal conflict.
Powered by Archecores, the Arche-Ymirus mechs and kinepolises were nearly invincible—especially the former. Scaffolded upon Ymirus mech frames, operated by controllers in whose veins ran the blood of the Ymirus—it might well have been said that the gods once again walked the earth.
But such power is not to be had for the asking. As industrialization powered by blue crystal took off on the Asgardian continent and Arche technology became increasingly well-understood, people began to consider the feasibility of mass-producing the immensely powerful Arche-Ymirus mechs as a way of gaining the upper hand in the struggle for power among the Eight Kingdoms.

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They turned their attention to the fragmentary Ymirus mech frames excavated from the ruins. While inadequate to resurrect Arche-Ymirus mechs, the incomplete frames could be mended, the gaps filled in with refined blue crystal. Further study of crystal runic diagrams led to the reconstruction of the body of the machine, which was then outfitted with a human-invented blue crystal steam engine powered by Y-thermoses—producing an armored mech that could be mass-produced. These became known as pseudo-Ymirus mechs.
Though they lacked the sheer power and the ancient sealed functions of the Arche-Ymirus mechs, in the absence of Arche-Ymirus mechs they were still quite effective on the battlefield.
But the connection between them and their controllers, lacking the augmentation of an ancient bloodline, was inferior to that between Arche-Ymirus mechs and their matched theonavs. Strengthening the connection required inhalation of refined blue crystal gas, with side effects for the controller. As a result, development moved in the direction of having a pilot ride inside the body of the mech itself.