A magical being, of which there are thousands. They fly around and use their powers to make unlikely sex situations happen. It's up for debate as to whether or not these creatures work for the greater good. For example, sex faries will have made it possible for the school geek to sleep with the school stud. Excellent for the reputation of the geek, but total social disaster for the stud.
Sex faries work better in situations where copious alcohol is applied to all parties, or when a high degree of lust renders the targets unable to function correctly. (Sex faries can be prayed to if desperate, and are more likely to exist than God)
-"Hey Steve, I hear you slept with Tina. What possessed you?"
-"There must have been some bloody sex faries in the air. I will never live this down"
-"Oh Magical Sex Fairy, please please PLEASE let me have one night with Danny, and I'll never ask for anything again, I swear!"