Shipping Meme! I remember this was done in other games a while ago, but basically people put up a pairing, either logged in or anon, and give a prompt for that pairing.

Then the people who play the characters can roleplay out a scene following the prompt! If one or neither of the players are up for it though someone can just write a fic or draw something. Multiple fills a-okay and fun and shenanigans are had!