A list of prompts for the cliché AU writing meme at DDD. ♥ Obviously, they're free use for anything else, too!
i. [cyberpunk]
Wikipedia article. To allow a broader range and less research, it's fine just to use the stereotypical idea of "the future"; incredible Artificial Intelligence, a barren planet of industries, being able to access the cyberworld through a virtual body - all of those kinds of things.
ii. [pirates]
Self-explanatory, as a lot of these are! Common stereotypes for the Pirate AU include one character looting the other character's village and kidnapping the other character whole they're there, someone sneaking on board a pirate ship and being reluctantly taken in by the crew, being rescued by pirates, or a general "We're pirates on a ship!" thing.
iii. [nobility&slave]
The good old-fashioned "so-and-so is the Prince/Princess of this land, yadda yadda yadda, now let's get you a pretty little servant for you to fall in love with". 90% of the time, they always run away with each other in the end because their love cannot be.
iv. [chibified]
Maybe only one character is the child, or maybe you're writing out a whole group of them in kindergarten! Whichever way, at least one character is now a child, and chaos tends to occur.
v. [high school]
If I have to explain this, I will be very disappoint. A lot of the time, it doesn't hold to a very realistic image of a high school, so it's up to the writer on whether or not they want to put limitations on it or not! Don't be afraid to stereotype it up in here, cliques are a very common plot device.
vi. [rock band]
This can be interpreted one of two ways; either it's a high school(/university/etc.) band that a bunch of friends have gotten together to perform at the latest concert and beat that awesome contest coming up, or one character falls in love with the gorgeous singer(/guitarist/drummer/not the bassist because nobody likes a bassist) of a popular band, and Mr. Hotshot Celebrity takes an interest in them!
vii. [university]
Again, self-explanatory. It's like high school, but worse. Or maybe better. It probably involves a lot more study sessions that turn into sex, and awkward meet-ups for coffee later.
viii. [space]
It doesn't have to be a Star Wars epic, but that's a good place to start. Insert character(s) into a setting where parties in the cold of deep space are a common occurrence, travel to other planets is so five thousand years ago, and tapping alien lifeforms is no longer a dream! Perhaps your character is the alien. Wars frequently come with this package.
ix. [historical event setting]
One of those pesky ones that requires research, unless you want to wing it. Characters are inserted into the American Revolution, or World War II, or any other major (or minor!) historical event - and often on opposing sides.
x. [timeskip]
Three years, five years, ten years later - we get a look at what life is like for certain characters in their futures. Surprises and plot-twists are optional.
xi. [genderswap]
Those two guys? Yeah, at least one of them is now a girl - or maybe both, if you'd rather. You can explore how that character and their relationships would be different if they had been born with different chromosomes, or maybe just general hilarity will ensue.
xii. [fairytale]
Characters are inserted into the roles of fairytale characters, and they play out that story, but with their own personalities substituted in to alter it; it's possible for that to drastically change the outcome of the story. The Little Mermaid isn't quite so sweet if Ariel is a psychopathic little girl.
xiii. [crossover]
Take a character, or as many characters as you like, and drop them into another series of your choice. Altered backstories can be as complicated or as vague as you like.
xiv. [harry potter]
Like high school, but magic. Broom flying, Charms classes, the Sorting Hat, magical candy - whether they're just starting their first year, or they're well into their wizarding career, welcome to Hogwarts School of Witchcraft and Wizardry.
xv. [powers]
Characters possess the abilities to change their shape, or speak to animals, or call upon the elements, summon fire to their hands, freeze enemies solid - all of those wonderful oddities and the splendid exile that comes with being labeled as a dangerous freak; or maybe a perfect weapon.
xvi. [modern-day]
Think of what you did today. That's the gist of it. Anything that your character would do if they existed today; it's a bit like high school or university, but focus on the aspects outside of the school-related things. Other than that, this is a pretty open genre.
xvii. [steampunk]
Wikipedia. A Victorian-looking time, where technology likes to run on steam and clockwork (Clockpunk is an acceptable alternative). Everything looks pretty weird and very 19th Century-industrial and almost futuristic, but in an old-fashioned, brassy way. Sky-pirates are not uncommon to add to this.
xviii. [illogical pregnancy]
What was that? Males can't get pregnant? Don't be silly, of course they can, because they just did. Exploring the world of your character having a child, through M-Preg (and F-Preg?) or religious (and/or Star Wars)-style of having no apparent lover or sexual relations but giving birth anyway. It's fine just to leave the icky explanations out and have a laugh at the little baby girl toddling around after your character.
xix. [supernatural]
Ghosts, angels, whatever you'd like to toss in here, it's a long list of possibilities. Finding and befriending/romancing a lonely ghost in a haunted house is quite typical, as is fallen angels and demons looking for some sin. Entirely supernatural worlds are good, too; for example, a world torn between heaven and hell, where both angels and demons reside.
xx. [arranged marriage]
"This girl you've never met before is going to marry you tomorrow. Doesn't that sound peachy-keen? Don't worry, though, you're guaranteed to fall in love with her once you stop fighting." For the sake of money, nobility, family honour - whatever the reason, wedding bells are ringing, and there's not really anything to say other than, "I do."
xxi. [western]
Shoot 'em up, cowboys! Stereotypical old-fashioned American western setting! Cowboys, sheriffs, swinging doors on all of your buildings - and good old incomprehensible slang and accents. There's never shame in playing off the classic of a pretty damsel getting kidnapped away from her father, the local sheriff, by some no-good varmint.
xxii. [role-swap]
Two or more characters all switch roles, and exploration of changed histories, personalities and relationships ensue. Most common is a switch with the main character, because it creates a lot of interesting differences.
xxiii. [post-apocalypse]
The end of the world has happened, and for some reason, not everyone is dead just yet. A small group of survivors who want to find civilisation have to learn to accept each other and work together in order to survive! Also, there might be zombies. Watch out for that.
xxiv. [mental asylum]
Self-explaining again, but let it be noted that your crazy house can be as unrealistic and abusive as you like; plots by the head of the asylum to exploit someone in some way are an old favourite. This can be a mind-fuck, a good old laugh of some crazies just trying to build a dysfunctional friendship, or an absolute tear-jerker. Oftentimes, one of the doctors falls in love with the patient and they break out together.
General hospitals are an a-okay substitute, but you have to remember that it's never lupus.
xxv. [prison]
Similar to the mental asylum, but this time, don't drop the soap. It can be an ordinary prison with a couple of messed-up individuals thinking they'll kill each other, and then finding out they're not so bad after all and plotting their escape together (or waiting it out, for a touching conclusion) - or a psycho prison like Deadman Wonderland, where the inmates have gladiator-like competitions for the entertainment of a screaming crowd.