Blackjack: Take your OTP and put them in a casino. Character A is an attractive Blackjack dealer. Character B is a determined gambler who can’t seem to stay away from Character A’s table.
Office Space Cheer: The characters all work in an office building. Every day, someone keeps on bringing in homemade food for the break room. Each time, it’s something that one of the workers particularly likes. Who’s bringing in these treats, and why?
Songfic: Write a songfic involving one or all of the following songs: “DNA” by Little Mix, “Opposites Attract” by Paula Abdul, and “Voodoo” by Godsmack. Have fun!
Killer Pet: Character A gets a new pet, which turns out to be a vicious beast. Does Character A know, or does the animal act innocent when they’re around. Does the pet secretly want to eat Character A, or is it fiercely protective of its new owner? Do the other characters figure it out, or is it only one character who knows? Does the killer pet become the ultimate protector, or the bane of everyone’s existence?
The Dragon and the Knight: Take your OTP. Now, make Character A a fire-breathing dragon, and Character B a knight in shining armor. Is Character B tasked with slaying Character A, or delivering them tribute from a fearful village? How do they fall in love? Can Character B shapeshift into a human-esque form, or is the romance more of an emotional one than a physical one? This can also work in a platonic sense, of course. I’m just a sucker for cross-species romances.
Keeping Cool: The characters of your favorite series are caught on the hottest day of the year with no air conditioning. How do they survive? Is there a pool nearby? Do they fight over who gets to hide in the freezer? Does a water balloon war tear everyone apart? Only you can decide!
Daemon AU: Based on Phillip Pullman’s His Dark Materials. All of the characters in your fandom have daemons (animal manifestations of their souls). What kind of daemon does each character have? How do the people and daemons interact? Do the daemons act differently toward each other than their people do, hinting at dishonesty concerning the characters’ true feelings? Imagine how the characters and world overall would be different because of this.