Satan is cruel and merciless. The stories of him are just as much, explaining all his past attempts to engulf the Earth in flames. He wants to watch our corpses burn to crisp. And he just might make that a reality - that could backfire real fast. Ever heard of a Gemini demon? It's like a sufferer of MPD, but limited to two alter egos. One personality could be a total badass, but easy prey for demon hunters. The other could be an exact opposite, sweet on the surface but possessing mind-boggling abilities. Their personalities are unpredictable, and to make it worse, they could switch up any time. It's what makes their kind the most dangerous, rarest, and - a goal for Satan.

Satan has already accomplished kidnapping an angel and joining its mind with his latest and most powerful demon, Dart, who has been wreaking havock on the villages, to make the deadliest Gemini demon in history. If he gets his hands on a legendary stone that has the power to mesh the angel and demon completely into one, he will create a half-demon, half-angel. It's up to the Demon Extermination Agency now, or Satan's creature will disrupt the balance.