Your and My Secret

A comedy manga by Morinaga Ai, of My Heavenly Hockey Club fame.

It stars a violent tomboy by the name of Momoi Nanako, and a shy boy by the name of Uehara Akira who has a crush on her. So far, normal enough. When Akira drops by her house to deliver some handouts from school, he gets mixed up in an experiment that Nanako's Mad Scientist grandfather was performing on her. When the smoke clears, they discover that Nanako and Akira have swapped bodies. Of course, they also discover that the machine that did it is trashed, and it's going to be neither cheap nor quick to get it fixed... not that Nanako's grandfather seems to be in any hurry to work on it.

For a variety of reasons Akira isn't very happy with the situation, but Nanako decides to have a bit of fun with it while they wait for the bodyswap machine to be fixed. They keep it a secret from everyone they know, but such major changes in their personalities certainly don't go unnoticed... fortunately, everyone involved (aside from Akira) sees it as change for the better and don't ask questions.

It has been adapted into a live-action movie.

Provides examples of:

 * Cut Short: Tokyo Pop, the manga company that distributed the English translation of the manga, went out of business in May 2011. Therefore, only 7 out of 8 volumes were released, leaving volume 8 untranslated and the whole English release unfinished.
 * Dirty Old Man: Nanako's grandfather.
 * Dogged Nice Guy: Senbongi may at first appear to be this, but he comes near to almost raping Akira several times.
 * Double Standard: Everywhere. It doesn't get much more blatant than the entire cast preferring both of the leads in each other's bodies. Apparently, a vice for one gender is a virtue for the other.
 * Ear Cleaning: Shiina did this once for Nanako's grandfather, whom he has a crush on.
 * Freaky Friday Flip
 * Man, I Feel Like a Woman: The thought crosses Akira's mind, but Nanako threatens to streak at school in his body if he does anything.
 * Masculine Girl, Feminine Boy: Akira and Nanako, initially. Once they're in each other's bodies they're just like a typical boy and girl.
 * No Periods, Period: Averted, and one of the reasons Akira isn't too happy about being trapped in a girl's body.
 * Nosebleed: Akira gets a few over Nanako's body ... while he's in it. A couple over Shiina, too.