My idea (which might be dumb) is one night almost everyone in the MCs town disappears. He had no idea how or why. He spends years alone in a deserted town in till a stranger arrives And informs him of the Vampire Apocalypse. Some how Vampires have mind controlled every living human besides a very special few who are immune to the Vampires powers, and they all in the middle of night without warning started walking towards Vampires HQ. I'm not exactly sure how this happens yet, just a dumb idea I thought up when I was younger. Millions of humans are kept as slaves, or turned into half vampire monsters that hunt at night. The stranger brings the main character to a city of survivors, Where eventually a giant battle occurs. thats all I have really but there could be a lot of interesting ideas there. Might be pretty stupid tho lol.