Nightwalker

Nightwalker is a term applied to non-human beings that live in the dark and cannot survive sunlight. Most feed on humans and also enjoy tormenting them. Nightbreeds, a type of minor demon, wish to survive in the sunlight. Silver appears to be dangerous to them as NOS agents use silver-coated bullets in their guns.

Types of Nightwalkers:
 * Nightbreeds - The most common adversary, these beings feed on human flesh and attain sunlight by possessing the bodies of humans.
 * Vampires - Vampires appear to be much rarer compared to other Nightbreeds, and only a few have been shown. They survive by drinking blood and a vampire can turn (sire) another human into a vampire.
 * "Urban Fairy" - Guni is the only known example of this species and calls herself an "urban fairy" despite resembling an imp. The official name of her species is unknown. She is the only known Nightwalker that doesn't eat humans or animals.