Centuries ago, vicious and bloodthirsty demons who were immune to all manner of weaponry plagued mankind. Humanity's cries for help brought forth the Idaten; battle deities who would use their incredible speed to hunt the demons down, and then seal them away. In the following 800 years of peace, the Idaten have not had any enemies to fight. But that is about to change...

What have the Idaten been doing in the eight hundred years without any demons to fight? Where do they come from? What is their true nature? And what are they going to do when Dr. Obami plots their defeat?