Demons have a human sized body with a knobbly spine, short tail and three pairs of limbs: four prehensile limbs and two large wings. They also have a long head with a blunt snout, consisting of a bat-like nose, eyes with vertical cat-like slit pupils set far apart on the head, and a large mouth with 4 primary teeth and several secondary teeth. The backs of demons are covered in sparse, short black fur and there are folds of skin on the base of the neck.
Demons don't have projecting ears, instead possessing ear-holes similar to that of reptiles, birds and amphibians. However, the demons possess hair while lacking feathers, scales, or beaks, suggesting a mammal origin. Their size, specialized predatory features, and vestigial (though still easily visible) tail make a bat ancestry less likely, and their legs are similar to feline or canine hind legs. Also, their roars strongly resemble those of a lion, tiger, or other large cat (as opposed to the screeching of a bat), and they possess vertical slit pupils similar to felines. These features, in addition to the layout of their teeth, would seem to support the possibility that the demons are descended from tigers, which were native to some parts of Russia before the war.