Genderswap curse-created girl!Dean Wincest fic FTW! Lol.
Not Time's Fool by FayJay - Wincest, set S4, long fic (21 chs), Author's Summary: A story in 21 parts, featuring an Ancient Greek curse, an unexpected metamorphosis, adventures in pool sharking, numerous shots of tequila, a nun outfit, zombies, angels, demons, kidnappings, startling discoveries about old acquaintances, massage, a game of strip poker, girl-on-girl action, girl-on-boy action, and boy-on-boy action. Despite my expectations or inclinations, it swiftly became clear that this story was going to be Sam/Dean. And, indeed, it is. Because my muse likes to fuck with me. It also features Girl!Dean - but don't let that put you off. It's still Dean, bless him, despite the sudden girlsuit.
Girl!Dean is still very very very much Dean. He is completely in character and awesome. Very few genderswap fics actually manage to achieve this, so kudos to FayJay. Also, HOTDAMN is she a fantastic writer. Absolutely awesome. The narrative is very well done, Dean's internal dialogue about his feelings about being a girl, and feelings about Sam, and etc etc are all true to Dean as well, and ALSO??? TEH PORN IS HAWT AND PORNY!! But also emotionally satisfying too. And Sam is A GOD in this fic! (Not literally, in case you were thinking, but y'know, GORGEOUS!)
So yeah, GO READ ALREADY!!