OK hear me out here I have a plot that's for a vampire x demon, yeah I know it's a strange combo but bear with me.
(Let's say for the sake of this plot that true vampires aren't made they are born. If you were made from a human you are weaker and considered lesser.) So take a random vampire. Who is he? He's a nobody, a bastard child, a mistake. He'll never be the head of a coven and he's considered just above human-born vampires.
Oh the things we do for love.
Because this vampire is in love, yes he is. He's harbored a love for a woman far more high-born than him since he first laid eyes on her. The sweet thing is that she loves him too. This spells out a tragedy but our vampire hero is desperate to win his heroine.
So he makes a deal.
He bargains away the soul of his first born child in order to change his fate, he'll marry the woman of his dreams, be head of the coven, and have all he ever wanted. He planned to tell his son of the deal when he reached maturity in the vampire world, around 21, but that never happened.
Struck down by a group of hunters while seeking a fleeing slave the oldest is confronted by the demon who asks, "Do you want to find your father's killer?" For this he has to give up his soul sooner, he will never rule, he will die after he avenges his father.
Ugh I'm too tired right now to write the rest, I hope this at least interests you. Night.