Well I guess it used to be whoever the fuck you wanted, but they changed the rules recently to get more people to drabble. SO. Now two randomly picked characters go head to head every week and for every drabble written for that challenge/theme, the writer gets to assign a condom/point to the character they want to win (it's all completely pointless, but it's fun).
Anyway, the character with the most points at the end of the week wins and gets to go against another randomly chosen character for the next challenge. And I guess if a character wins three weeks in a row, they have to sit out.