This universe is comprised of a duality, akin to a reflection, with two dimensions fused as one. The first dimension houses the human realm, Assiah, while the second is home to demons, Gehenna. Ordinarily, communication or transfer between the dimensions is implausible. However, the demons can infiltrate the human world by overtaking any entity that exists within it. Satan, the deity of demons, is lacking one crucial element to exert control - an entity in the human world that can contain him. As such, he sired Rin, a hybrid offspring of a human woman, with the intention of using him for this purpose. Yet, will Rin accept Satan's plans or become a different entity altogether, perhaps an exorcist?