Because this is AIF, you can have plots that actually move forward due to sex(ual things). E.g. Rogue Cop, where sex opens a witness up, or HI's modeling for Wynne. In some sense, this and sex-based puzzles are what make it AIF rather than IF with some sexual encounters. An example of the latter is INFOCOM's Leather Goddesses of Phobos, which could be played in "tame mode", i.e., with no sex. Or I-0.
A number of authors say that having sex with as many people as possible shouldn't be the whole point of a game, that there has to be some other plot that gives the character a goal. This is a good point, though it can be debated. Here's how H_Slave puts it:
The best hook for making the game believable is to make sure that the player isn't even thinking in terms of "the hunt". Give them a goal, give them a story, and let the sex come to them. Also, it can help to put a significant divider between the fulfillment of a goal and the reward. Say that, at the beginning of a game, you get the option to rescue a woman. No sex scene, no quickies, just move on with the game. Make that action pay off, say, three scenes later, where your mercy (that didn't have to be given (i.e. it wasn't the primary goal and wasn't required to achieve that goal) gets you some...err..."preferential treatment." 8-) Or, to be even more cruel, keep giving the player the option to screw her as the game progresses, but make the sex sweeter the longer you wait. After all, a woman isn't gonna be into sex if it's the price of her freedom...but afterwards, when it's freely given, it would be better...or better still if you get to know her better...and better yet once she's fallen in love with the handsome and virtuous hero.
As described in the sex chapter, different plots leading to sex can make the sex more interesting. In addition, they can make sex much more believable. In almost any game, the character needs to do something before having sex, whether it's drinking a magic potion, or dancing with the NPC. In other games, the process of getting to sex takes longer. Whichever way it's done, strive to make the character believe that sex could occur in that situation, which will help mimesis. (BJD doesn't really do this, but that's sort of the point of BJD.)
The good news is that AIF players will tend to be pretty forgiving about plot. They have no trouble accepting the idea of a virus or potion or creature that makes every NPC a walking hormone. (The PC is of course a walking hormone already, or he wouldn't be playing AIF.) But having a little explanation is much better than having none.
Branching plots can also help replayability. H_Slave gives the example of a hentai game where there are three different girls. You have sex with each of them, but then can decide which one to "woo", and you get to have more sex with that one.
Finally, branching plots make IF more fun, because they give the player more feeling of control. If every choice in the game is either wrong or right, then the game isn't much different from a book. The author is herding the player from puzzle to puzzle, forcing him to read each scene in succession, preventing him from ever moving away from the linear plot. Of course it takes much longer to write several completely different stories, but even small divergences can give the player the feeling that he's the one controlling the action.
NewKid has said he tries to give his characters different driving factors. This makes sex with each one different, even if the actual sexual actions are the same. These motivations might include loneliness, manipulativeness, or gratitude. Love could certainly be an interesting motivation, but it's a challenge to code convincingly. What does the NPC like and dislike? What are her short- or long-term goals? Give each NPC a history that will explain the way she acts. You'll find that this will help you write dialogue, actions, and sex scenes for that character.
The good AIF games have several unique characters, not just anonymous women you can screw. RC's Tabitha has an interesting quirk. And HI's Muffy actually undergoes some character development over the course of the game.
Many AIF NPC's can be pretty simple, because your interaction with them is limited to a couple of basic interactions plus a (perhaps extended) sex scene. However, you may want to create a game in which there's a "main" NPC, like HI's Wynne. This character would be the main focus of the game (even if you "interacted" with some others), and you would have a number of (erotic and non-erotic?) scenes with them. As a basic rule, the more time your character spends interacting with an NPC, the more time you need to spend on developing them. A main character will need more than just a simple motivation, like greed or loneliness may be best to come up with a history of sorts for them. You should almost certainly have more notes about a character written down somewhere than there is actual text about the character in the game.
Historically, many authors chose to write xtrek, i.e., to use Star Trek characters as NPC's (and sometimes for the player as well). This allowed the game author to take advantage of years of Paramount character development. Many argue that this is less work. NewKid, on the other hand, says that "Established characters require less establishing material, but they are necessarily limiting, and often require more work later to get around the stuff you just didn't write. (Of course you can just change what you don't like, as in making Troi a nymphomaniac.) An original work lets you shape the world and characters however you wish (Follow Mimesis folks!), so many things are easier." And if you have to change a great deal of these characters' personalities, maybe you should just create original ones in the first place?
One of the best ways to make characters realistic, by the way, is to give them a wide range of actions aside from sex and/or the exact actions needed to solve a problem. Characters can move around and act while the player isn't even there (e.g., Moist's Fanny). Many characters have "atmosphere" daemons, little actions they take while they're in the room with the player but he's not interacting with them. (For example, "Belinda sulks in the corner.") These little actions can remind the player that the NPC is there, but they can also add to the NPC's personality - especially if there are several different possible actions (which you can pick from randomly or depending on the current game state). Finally, characters can react in certain ways to actions the player takes: if the hero finds a secret door behind the bookcase, won't his girlfriend be intrigued? Even saying "Wow!" is better than nothing, though perhaps not as good as "Bobbi stares vacuously at you. 'Is that supposed to be there?' she asks?"
The player has only a few hours of playing time to get to know the NPC's. But there are several methods for building the player's relationship with them.
Historically, the first way this was done in AIF was by writing xtrek games, However, this does have some drawbacks. First, a player might not watch Star Trek much, or (if that's too hard to imagine) might not know anything about that obscure character you're using who appeared in only four episodes in the second season. A more significant drawback, for some, is that this gives the author much less room to create new and interesting characters.
Another way to build a relationship is just to remind the player when they first meet the NPC about their prior relationship. Here Doppelganger proposes the opening text for your meeting with a character in an X-Men game:
You find it difficult to comprehend that the X-Men have allied with this man. Though he insists on using his alias of Michael Xavier, you also know him as Magneto, the would-be world conqueror. He is quite a bit younger than you had expected him to be. You vaguely recall something about Magneto being rejuvenated in some manner. Nevertheless, he exudes an aura of confidence that could only come with many years of experience.
A surprisingly simple method: use characters that the player will automatically realize he should have a relationship with. Arkane made this one up spontaneously:
Well you came home after a long night a work, trudged up the stairs without turning on the light, proceeded to get undressed and turned towards the bed. It was then that you saw all the candles, and your loving girlfriend laying there waiting for you in a black silk negligee.
Finally, you can actually try to build the relationship during the game. This is tough, since the player probably isn't thinking about falling in love with an NPC; they're too busy solving puzzles and finding people who are easier to have sex with. And you don't have too much time or text to do it with. But many people give Planetfall's Floyd as an example that developing a real relationship with an NPC during a game is possible. If INFOCOM could do it, so can you! To do it, you'll have to carefully orchestrate the interactions between the NPC and the player throughout the game. See also the "How to Write Romantic IF" thread and the game "Muse". Of course, depending on your plot, the player may not have to actually fall in love with the NPC, just in lust, which is considerably easier!
