What should my book be about

If you want your book to be similar to the ones you mentioned it would be more within the action or adventure genres. All good stories have romances in them. Not all, but a lot. I think you should write whatever you feel led closest too and see where it takes you. Who knows, maybe you'll start on a dramatic and action packed romance and it might lead you into the characters becoming vampires. And that might only set off the path of starting a series or trilogy. It all depends on what you feel you should write. It is your story and your imagination. Let it run free!
I hope I could be of some help. Good luck with your book!!!