JYB ~Mehame Haruuga wa Himitsu no Jumon~

The game's hero, a young man named Otomegawa, encounter Chururu, a cheerful female magical creature, who accidentally curses him to become a woman. Only the princess of the Magic Land can lift the curse. The princess has been reborn as a human being and is currently living on the Earth. The problem is that as a human, she has no access to her magical powers that would help Otomegawa solve his predicament. Only a moment of true ecstasy (and since this is a hentai game, we all know what it means) will awaken her true potential! Luckily, the princess also happens to be lesbian, which perfectly suits Otomegawa's current condition and the means necessary to achieve the goal...

[Edited from Mobygames]