Heian-kyou, capital and the center of elegant, aristocratic culture, is heavily guarded by a spiritual force field made by court mages -- or so it seems. In reality, the onmyouji can only defend the palace located in the northern part of the city; in downtown, monsters known as "horrors" that feast upon human souls roam after sunset. There are, however, a group of heroes protecting commoners from these horrors in the darkness.