Xion

Xion is a lazy Mary-Sue that no one REALLY likes. They just like to put their brain in her body--normally this ends in whiny fanfiction--and fulfill their sexual fantasies with whichever member of Organization XIII that tickles their fancy. This, of course, excludes Vexen, Lexaeus, and Xaldin (since they're not considered pretty enough, when really it's because they know how to kick some ass).