Gehenna, and Assiah, mirror images. Assiah, the human world, lives in ignorant bliss of the demonic forces that take advantage of every single aspect of their world, all but for the True Cross organization and the many Exorcists of the world that fight to protect their home from the forces of Gehenna and Satan's constant push to exist on the mortal plane.
After the Blue Night left many religious groups crippled, the True Cross Academy started to flourish, taking more and more students that wanted to take the fight back against the demonic forces. The twin brothers Yukio and Rin live in this world, key pieces in the fight between the two worlds. These Princes of Satan, born with their demonic father's blood and to a human mother, may be the world's last hope… or the harbringers of its destruction.