Although vampires are not the blood-sucking, human-devouring monsters told in the continent's stories, one must understand that such tales must come from somewhere.
The stories that describe them this way date back centuries, when powerful vampires were still abundant and could move with impunity, causing havoc, but these were not the truly feared ones.
In the past, the blood eyes that Zaros possessed were not so rare. Certainly, not every vampire had them, but at least 1 in 1,000 possessed these eyes. The blood eyes of vampires not only serve to see things beyond the ordinary, as Zaros used them to discover that Andrew is a candidate to become the god of Eros, but they also have other abilities, which are not very pleasant.
