The first and most powerful vampires turned through a modified Immortality Spell meant as a protection against werewolves.
It was euphoric. The feeling of power was indescribable. But the witch Ayana was right about the consequences. The Spirits turned on us, and Nature fought back. For every strength there would be a weakness. The sun became our enemy-- it kept us indoors for weeks. And though my mother found a solution, there were other problems. Neighbors who had opened their homes to us could now keep us out. The flowers at the base of the white oak burned and prevented compulsion. And the spell decreed that the tree that gave us life could also take it away... So we burned it to the ground. But the darkest consequence was something my parents never anticipated-- the hunger. Blood had made us reborn and it was blood that we craved above all else. We could not control it. And with that, the predatory species was born.
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Rebekah Mikaelson about her family's transformation into vampires