Blade: The Series (2006)

Krista Starr returns from military service in Iraq to learn that her twin brother, Zack, has died under mysterious circumstances. Her investigation reveals that Zack was a "familiar" - a kind of indentured servant who agrees to do a vampire's bidding in the hopes that his "master" will eventually reward him with eternal life. Krista's search for her brother's killer soon brings her face to face with Blade, as well as with the killer himself, Marcus Van Sciver, a powerful vampire and high ranking member of the House of Chthon. Smitten with Krista, Marcus decides to turn her into a vampire by injecting her with his blood. Krista is then approached by Blade, who injects her with the same serum he uses to control his own vampire instincts, and offers her a chance to help him avenge her brother's death and bring down Marcus and the House of Chthon, and revealed that Zack was trying to do a sting operation with Blade. The two form a reluctant partnership.