In ancient times, Satan was defeated by the gods in the War of Armageddon and was sealed away deep within the earth. But in the modern day， Satan once again aims to control all the universe - and towards this aim, his Devil Siders have begun to act! But now the child born between the worlds of gods and demons, Reiki Kikoku, has joined forces with the God Siders to destroy the demons!!

(Source: Book Walker)