The nature, purpose, and agenda of the Other Power are perhaps the deepest mysteries of the MGP universe. Despite the far-seeing, near-omniscient of Fate to see the future, she cannot at all predict the movements or understand the nature of the Other Power. Even the High Spirits, the supernatural entities worshipped by the Ardent Empire who are tied to positive emotions and arranged the reincarnations of the Spirit Guard, could not give the Ardentia clergy any information about the Other Power. The best they could do was slow it down through their direct influence.
It is unknown if the Other Power is an army, a singular being, an anomaly, or even if it is anything we can normally comprehend. All that is known for sure is that it appears to somehow operate outside of the known multiverse’s usual rules and that wherever it goes, everything perishes. The first known activity of the Other Power is when it descended on the fragments of the Ardent Empire during the Ardentia Civil War. Because of its unforeseeable arrival, it guaranteed there were no victors of the war and the Empire was annihilated.
The very existence of the Spirit Guard is due to the actions of the Other Power during the Ardentia Civil War. The Princess formed her team with the express of purpose of protecting prehistoric Earth (which they called Terra) from annihilation at the hands of the Other Power, or the despotic rule of The Empress. In the final year or two of the War, The Scholar devised a method of scanning the veil surrounding the other power and, through application of an empathokinetic device, subtract out the veil’s influence. This allowed her to gain brief glances at the “horrors beyond the veil,” and to design foci capable of actually fighting back against the Other Power. Though this has been revealed in the only vision Robynne Darling has had of the Shrine Maiden, in which the Scholar also featured, these revelations have yet to be revealed to the reader.
Unfortunately, the foci take so long to make that he Scholar was only able to make five before the final battle. That amount of time was not enough to make a difference in the Ardent Empire’s struggle against the Other Power, but the past lives of the Spirit Guard hatched a plan to protect the Earth from the Other Power when it arrived. The Shrine Maiden arranged for the five of them to be reincarnated as humans on Earth (the Ardentia were also human), and they stored the five foci created by the Scholar in the iris of the Gateway on Earth. There they remained for millennia, until the Other Power apparently began to draw near Earth and the Princess’s team was reborn as the Spirit Guard.