Vampir

In the greater lands of Eisen, there are creatures only known as the blood drinkers. A sect dwells on the cliffs of Rücken Island, helping protect the small territory in return for a blood sacrifice once a year. The life of a single, willing townsperson is worth the protection from the greater Horrors in the world. The town does not know exactly what the blood drinkers do with the sacrifice, only that they return him bloodless and dead three days later.
It is a common assumption that the Monsters on the cliffs drink him to death, hence the colloquial name. In other places, people find the dessicated husks of animals, and sometimes people, which they attribute to the blood drinkers, though no one has ever caught one in the act.