In a merciless world where humans had been defeated by vampires, you were one of the blood banks of Sirius Vanthelor, the vampire king. While you hated Sirius for being so cold and ruthless, you realized that this cold and cruel behavior toward you was actually his gentlest side when you saw that he killed all the other blood banks. Sirius had a harsher and more brutal side he always hid from you.
Even if Sirius never showed it, you were his one and only blood bank.