Concept: in a setting where vampires exist and can only be harmed by symbols of faith (crucifixes, etc.), a James Randi-style skeptic/supernatural debunker witnesses his family murdered by vampires, and dedicated his life to hunting down what he believes are a cabal of ordinary serial killers with a blood fetish and some cheap plastic fangs. They die when he shoots them with an ordinary gun, granted holy status by the sheer force of his belief that they are actually just ordinary humans who will die when shot.
The reason the sun burns vampires is that all the plants worship it.
That is the single most insane addition possible and I love it.