One of the aspects of gaming that gets poked fun at is where gaming approaches more serious matters. Everyone - more or less - has seen a video with a geeky teenager asking if there are any girls in the bar because he wants to do them. And a lot of games stray away from topics such as sex and such to avoid this. Sex makes us feel awkward. Violence is fine, but sex? That's a no go. This isn't something to make fun of, but just an aspect of our society. And one that is stronger in the U.S. than other parts of the world to varying degree. Still, what if you want those more mature elements in your game? What if you want your world to be a bit darker, a bit seedier. What then? Today I want to talk about that.
Fade To Black
One thing to remember is you can have all sorts of sexy, raunchy, seedy stuff in your game and still never have them at the game. My last few games with my group have run very much like HBO shows with as much sex as violence depending on the character. Just, unlike HBO, the sex never happens at the table. My group is old, mature, and comfortable enough around the table that we can RP up to the event, cut, and discuss only if important to the game as a whole. The amount of times that discussion has to happen is rare. Just as the amount of times RP goes beyond "we find somewhere private" from a normal scene. I say rare because for the most part just the fact it happened is all that is relevant for the story. Sometimes more detail is needed. Your group's mileage will vary from mine.
Fading to black is your best friend for almost any scene that would guarantee an R or NC-17 rating on a movie. Be it torture, sex, or real violence - you know, the kind that makes people uncomfortable.
Everyone Has Needs...
The first thing you need to know when trying to add these seedy elements to your game is that everyone has needs, and while those needs are more varied for certain groups more than others, they're still there. As a rule throughout history and fiction the wealthier and more powerful the group of people, the more deviant and depraved their entertainments may be - but that doesn't mean exceptions don't exist among less powerful and wealthy. Just think through movies you've seen: how many underground fight to the death rings have you seen owned by faceless wealthy? What about other things?
Now I said the first thing you need to know is 'everyone has needs' but in fact it is 'Everyone has needs, and someone is going to profit from it.' Where there is a thing wanted, there will be someone offering it for a fee. This is how you have brothels (both low and high end.) This is how you have people who will hold and train pit fighters. This is how you have people who will grab people to be said pit fighter.
Where There's Money There's Organization
The next thing to realize is that where you have money being made, there will be organization. Money will bring about someone trying to control it. That control will require establishing order. That order will involve jobs for people to do the services the money-making needs to function, and to bring that money up to those in control.
And money does go up. The more money being made, the higher it will go. The wealthy won't let it be controlled by other than them. And eventually the money will cross paths with the otherwise law-abiding folk - though maybe that should be in quotes. At a certain level you need to have the local law on the payroll. At a certain level you need to have arrangements and deals with those in charge of the law. At a certain level you need to have arrangements with the people who control the city or land on paper. And those things will happen.
Flesh Out As Needed
What this means if you can - and should - flesh out your seedy underside. You can go as in depth or not as you want, but I'd recommend knowing some stuff at the very least if you're planning on it being part of the game. That local brothel that maybe the PCs frequent, or don't, is going to have an owner. That owner will likely have muscle to guard the place and a means of moving money from the brothel to them - or to the next person up the chain. They'll also likely have relationships with other businesses for needed things - laundry, food, drink, etc.
Give it some work and you'll have yourself an underworld.