Welcome to the Pairing List That Ate Fandom Fic Community.
The Pairing List That Ate Fandom was introduced by apocalypsos, and basically takes the concept of picking two character names from a hat and writing a love story about them and crosses fandoms with it. (Which is how you end up with pairings like Captain Kirk/Buffy Summers, Jareth the Goblin King/Rupert Giles and Sarah Connor/Joe Dawson.)
To get some idea of what they look like, the first eight rounds of the list can be found here:
Pairings as seen on the list are exactly as pulled from the hat -- the only veto power comes when a pairing from the same fandom gets pulled. And hell, we can always see that, but why not see a vastly more frightening love story like Leia Organa/Cthulhu?
The rules for writers are simple --
1. There are no length requirements. Write a drabble, write 100,000 words ... whatever works for you.
2. Make sure to LJ-cut your story.
3. Stories MUST be of a romantic and/or sexual nature. It's called a "pairing" list for a reason. ;)
Any other questions can be directed to apocalypsos or muffytaj through theirs LJs.