Pick 5, 10, 15, 25, 50 or the full 100 prompts from a table. With a nice shiny banner as a reward for completing it.
a 100 word min limit with no upper limit.
Obviously with only a few characters in the fandom there would be no limit to the number of ppl claiming a charrie as no two ppl would write exactly the same thing.
Just thought it might keep the fic coming.