Hiromi Ichimaru is excited because her cute boy cousin, Makoto Kashiwagi
is coming to live with her. They'd met nine years previously when they were both six and Hiromi was visiting her grandfather who Makoto was living with then. Buuut, Hiromi gets a bit of a surprise, when Makoto arrives-Makoto's a girl. Well, not exactly....
Makoto is a hermaphrodite! The manga chiefly concerns Makoto trying to get through her teenage years with both sets(and both are fully functional-she has her first period and wet dream at the same time.

You lucky dogs who live in Japan can pick it up at the local manga shop.
The first four volumes have been released, and it's currently being serialized in Ultra Jump. For those of us who are outside Japan and are still deficient in our Kanji and Kana comprehension, you can check out free scanlations of the first 12 chapters(Volume 1 and 7-12 of volume two here: http://www.adtrw.org. (Btw, this isn't a commercial, I just love the series and like to spread the word about it.)