I knew I wanted to answer this question as soon as I read it. And the books I'm thinking of are my paranormal romances. Allow me to explain.
The next morning I began to research Mayans. Why? I've dreamed up story arcs before, but never had a character spoken directly to ME, the author. What I learned was that the Mayans had many rituals for their religion, and all of them involved blood-letting. The rulers would appear in public and prick themselves with knives and spears, or pull thorns through sensitive body parts, to collect the blood in containers of various kinds. Why? Well, if their rulers were vampires... The story wrote itself after that. I even used a few Mayan gods' names which I have no idea how to pronounce.
For added realism, since Keesha is a neuro-biological researcher, I knew she'd wonder what causes vampirism. I had her discover spores that are in the blood stream of all vampires. These spores can travel through space as dormant space dust. If they land on a planet with no iron-based blood-based creatures, they remain dust. But on planets with iron-based blooded animals, they can quickly invade the bodies and take them over, refashioning them into vampires who need to consume blood to survive. Gross, but the whole eternity thing is a real bonus.
I guess that's just the way my mind works. I've always enjoyed reading paranormal romances, but I never thought I'd write them, because I'd want to know the hows and the whys of their existence. Hopefully my readers enjoy my attempts to do just that.
How do other authors answer this question? Head over to them to see.
Skye Taylor http://www.skye-writer.com/blogging_by_the_sea
Victoria Chatham http://www.victoriachatham.com
Judith Copek http://lynx-sis.blogspot.com/
Diane Bator http://dbator.blogspot.ca/
Dr. Bob Rich https://wp.me/p3Xihq-1ZR
Beverley Bateman http://beverleybateman.blogspot.ca/
Rhobin L Courtright http://www.rhobincourtright.com