Heretics are a complete aberation of nature. Before they are turned into a vampire, they are born as witches without the ability to generate magic. Despite their misfortune, they were also born with the ability to absorb magic from other sources such as a dark object, a witch or any other supernatural being.
As a witch turning into a vampire, they lose the ability to generate magic and their connection to nature, for a witch is a servant of nature and a vampire is an abomination. But for a siphoner, since they posses no such ability, as they turn they can siphon on themselves since their vampire nature is a cosmic source.
Thus begins the new and rare vampire-witch species formerly known as Heretics.