Eleven years prior to the story, in a disaster referred to as the "Great Catastrophe" Earth's magnetic field shifted devastating significant parts of the world and killing off many of its inhabitants. Along with the disaster came the return of the Shadow Angels who had been in slumber in their city of since their battle with Apolonius. The Shadow Angels began invading human cites to harvest human beings, dubbing them "the wingless ones," like cattle, to extract from the captured humans. Their prana serves as energy and nutrition not only to the Shadow Angels, but also to the legendary . The Shadow Angels facilitate their harvesting via giant, floating harvesting machines called which are guarded by giant mecha called . They are sentient machines, yet there are times when they are piloted by Shadow Angels.