A few ideas for RPs to consider, with themes of crossing over lines you thought were sacrosanct and discovering it's actually really easy - with questions of what else could be crossed.
In the Line of Duty
Rating - Light to Bon
Pairings - Russian Mafia Underboss and Undercover Policewoman
You got a special assignment right out of the academy, something they couldn't trust with the normal undercover officers. He seems to have eyes and ears everywhere and he's sniffed out 5 undercover officers already. This time they have to play it extra careful.
His name is Yuri Garganov, an up-and-coming Underboss with the Russian Mob in your city. A rising star in the organized crime scene whose recently been tagged by the aging Boss to replace him, Yuri's future in crime looks bright indeed. Which is why he's got to be taken down. It hasn't been easy though, he's nicknamed "The Serpent" for his knack for finding and exploiting less then loyal members of other organizations including the police and he's already used them to locate and foil every previous attempt to get an undercover officer on the inside to take him down.
You were chosen for three reasons. One is that you're so new that you don't have established connections in the force yet, so whoever is Yuri's mole in the police can't finger you. You're also the first female undercover officer they're going to try on this and Yuri is used to male opponents. You're also exploiting what's considered Yuri's number 1 weakness - his fondness for women as word on the street is that he's had a shocking number of sexual partners even by crime lord standards.
And the plan will go very well at first, but Yuri isn't stupid. One night it goes so far that you end up having to have sex with Yuri to maintain your cover - and while you've heard rumors about this too discovering first hand Yuri's "Serpent" was more then you expected. In fact, Yuri easily gave you the best sex of your life...
Rating - Light to Bon (NC-by-Deception or Blackmail possible depending on tactics used).
Pairing - A Superhero or Superheroine and their Archnemesis
The Archnemesis is a unique relationship in the superhero and supervillain world. Two people so set against each other that it starts becoming difficult to define one without the other, and you happen to have one on your own.
Things take a turn for the worse when the supervillain discovers the identity of the other. While trying to figure out how to use the knowledge, what was going to be a one-off sexual whim becomes something more when the pair of Archnemesis discover just how well their sexual chemistry works together.
Other Notes: There's a bit of flexibility of who is the hero and who is the villain, but the basic idea will be that while they hate each other on the battle field they discover that they have amazing sex together.
Name, Rank, and Serial Number
Rating - Varies, Negotiable
Pairing - An allied POW and a female SS officer
It's in the Geneva Convention that a Prisoner of War doesn't have to say anything when interrogated. Just name, rank, and serial number. This one has been a particularly tough nut to crack, and so they gave him to you. One of the Reich's most successful interrogators ever, the idea of a prisoner - especially a male prisoner - withholding information from you is laughable.
And yet, as the days pass and still all you can get from him is his name, rank, and serial number you start shifting tactics to try to seduce him for information instead, and it starts to backfire.
Other: This one might get a bit touchy, admittedly. Right now I'm picturing something like she tries to get him to talk with her sexual wiles but he turns that on it's head. Might go as far as he rapes her during a power outage- and she likes it. In the end, Allied dick overpowers her Nazi resolve.