Stamina challenge

You read the card that your fate leaves you with... one reading "Stamina challenge". You're confused, will you just have to run a mile or something? No no no, one of the girls casts a magic ball that hits you, making your clothes disappear, no sooner your body shrinks and your chest grows, your proportions become more feminine while your hair grows and manhood decays. The girls explain that the sorority picks some of the hottest guys to invite over for a stamina test, where they see which of the girls can last the longest in a huge sex-fest. They explain that if you last the longest then they'll change you back, if you fail... well there's always next year.