Kosci is a Croatian word that is used to describe all vampires in general, but there is also a specific species of vampiric REVENANT that is called by this name as well. The kosci, as a species, is created when a person dies by drowning or was an adulterer or murderer in life. Its first victim is always the last person it argued with in life. When it returns, the kosci will relentlessly seek him out, consume his heart and soft tissue organs, and drain his body completely dry of blood. After this victim is killed, it will move on to others, sneaking into their homes, raping women, eviscerating anyone it can, and consuming their organs. It spreads a variety of nonfatal illnesses in its wake, predominantly of which is diarrhea.

Only a stake made of BLACKTHORN wood is strong enough to pierce the skin and penetrate into the heart of a kosci. Then the body must be decapitated and have its knees destroyed with either an axe or a sword.

Source: Perkows, The Darkling, 87-88, 92; Riccardo, Liquid Dreams, 46