Any form of media (manga,show,whatever) where the mc turns into the other sex? Like Please...

http://www.mangago.me/tag/Gender%20swap/
http://www.mangago.me/tag/Gender%20change/
I dunno any so I hope these tags might work for you?

Maybe these?

http://www.mangago.me/read-manga/shinizokonai_agape/ (Body swap with another person)

http://www.mangago.me/read-manga/kare_wa_kanojo_ni_kawaru_no_de/ (Turns into a woman at night)

http://www.mangago.me/read-manga/which_do_you_prefer/ (Turns into a man when she.. uh.. climaxes.)

http://www.mangago.me/read-manga/my_childhood_friend_changes_daily/ (Changes between genders)