Every thirty days, there is an eclipse. Genosus, The Unconquered Sun, goes silent and dark, resting in His temple. For a full day and a full night, there is no light, no sun, no morning and no night. Aside from the great troubles this causes Kesh Farmers (who must endure a 24 hour siege by their own crops) it also permits forces of darkness from out of space to influence the world, where once they would have been held at bay by Genosus's light.
The Dark Watchers appear as black shapes that blot out the stars in their wake, and they descend upon the land on the eclipse, and drift overhead, perilously close, sometimes so close that their tendrils touch the ground. Every culture has rituals and practices to drive away these great terrors during the Eclipse. The Genosians have their Feast-Days, raising great bonfires and holy shouts. The Dessians in general keep the Watchers at bay by singing in choirs. The Karthacki have an additional defense, for they have contracted with The Ur-Grue, Master of Darkness, and so the shadow is as thick as stone to the Dark Watchers, and they cannot approach. Pagans rely on sacred runes set upon their homes and branded upon their cattle to proof them against harm. The Zells do nothing, for the sea is theirs, and the sea keeps them.
Sometimes, however, whatever the precautions, The Dark Watchers leave something of themselves behind. These are called Spawn, Demons, or Terrors. Agonized by the touch of the sun, hopelessly insane, maladjusted to the world upon which they have been stranded, and alien to all interaction, they are monsters that must be destroyed or driven away by the inhabitants of the land. Each kingdom has a force tasked with hunting down these demons. Krajina has the Unkindlies, Dace's Volkodavs double for the task, and Solar Illegon and the Kaselreich have The Sphalerite Order, just to name three.