Gamindustri: One of many parallel universes protected by four goddesses known as CPUs. Long ago, these four CPUs engaged in a war for supremacy known as the War of the Guardians. However, this war weakened their protective hold on the world inhabited by their people, and in turn it was flooded by monsters under the influence of an individual known as Arfoire. During the War of the Guardians, one of the CPUs—Neptune—was defeated by the others and hurled down to the world's surface from the heavens. The drop caused Neptune to lose her memories, as learned by Compa and IF, who happen upon the fallen girl. A mysterious book containing knowledge of all Gamindustri's history suddenly speaks out to Neptune, Compa, and IF. With the assistance of this sentient book, the trio embark on an extraordinary journey across four different nations on a quest to save the entire world!