They covet it, drink it--exist because of it. Were they not to sup on blood they should be destroyed.
It is their staff of life, the sole reason they go on. It can come from any living creature, but it is sensual with a human victim.
It is a pleasurable thing for a vampire. Feeding is sexual in nature, if not for the victim, it is for the vampire at least in my fiction and especially with the character Eco who appears in two novels.
Feasting on blood while sexually enjoying someone is the height of erotica I think. The victim may pass from life to death, yet as depicted in much vampire fiction, that victim is beguiled and bled to death at the same time!
And yet, as the vampire feeds he suddenly becomes aware of his victim's mortality. Should he or shouldn't he? How great to be like a god! A demon of the underworld permitted to make such a decision: creation or not.
Existing undead or to lie forever mouldering in the worm-ridden earth.
The victim sinks to the floor and the vampire follows. Then raising one, nearly bloodless hand up to its mouth the vampire kisses it.
"I shall not destroy you!"
The vampire tears his own flesh open and reddens the victim's white lips with his own blood.
Eyelids flutter open and the vampire can see his own kind staring at him.
"Come forth to dwell in the world of the undead!"
And so the newly created kinsman goes forth to seek the blood and the sin of its new heritage, to dwell amongst the undead, never aging, ever young, forevemore...!