Vampires but not as you know them. London (I'm British) would be a good setting. Everything is up for discussion, this is just the idea as it stands.
Most vampires are ancients who were turned a very long time ago. Turning people just adds to the competition. Many newer vamps were turned so they could be servants to older houses, this backfired however when a certain smoking hot vampiress (you) led something of a rebellion. Now these younger vamps were their own faction, but have now split into two.
Faction 1 are guilt-ridden about what they've become. The have recently outed the undead community to the public. They wear black ribbons because they have sworn never to feed on living flesh. They now subsist on blood from abattoirs and are prominent in the media. They are trying to reintegrate into society, taking night work or setting up patrols to protect the humans.
Faction 2 (your faction) are adapting to humans knowing they exist and how to kill them by burning the old guard's quaint little rule book. They can be as brazen as they want to be, all their wildest desires let off the chain. They've declared open season on the human population. They're adding to their numbers carefully selected psychos, people who own clubs and hotels, anyone useful. They want to increase their numbers until they can claim supremacy over the old guard - at least in Londonl. You're their leader.
My character is human. She has some wiccan power but is struggling to harness and control it. She has acquired only one text that has proven useful and has no clue where else to look. By feeding on her, you can harness this latent power. No one will dare challenge you. Wiccan blood is on the decline, so this girl is a rare find. You quickly become physically addicted and it can take all your self control to prevent you from draining her when the thirst sets in.
You are going to keep this girl as your pet. You have a careful line to walk in helping her to develop her powers but keep draining her so she can't overpower or abandon you. In time she will become your loyal little slave but that will take a lot of work. To begin with everything is very non-consensual. The girl claims not to be bi, has only been with men but you'll soon persuade her otherwise. In the long term, the addictions run both ways and together, you are invincible. It's been a long time since you had to give thought to basic human needs like food and warmth however and especially to begin with, you can be a little forgetful. She better learn to hold your interest.