Ranma 1/2
My guess is Ranma 1/2 is Rumiko Takahashi's most popular manga and anime, and this is saying lots, because Rumiko Takahashi has done lots of mangas. And Ranma1/2 is my guess is the most popular gender bending manga ever, which is still saying lots because the Japanese seem to want (need?) comics with gender ambiguities. Hey, who doesn't?Ranma was originally a fairly normal boy, except for being a martial arts protegy, but that was no big deal, it ran in his family. It was during a training tour in China Ranma acquired a curse, that is really not so bad. He turns into a girl when dowsed with cold water. Mind you, he back to his boyish self with a splash of warm water. Of course, Rumiko Takahashi , being a bit cruel like all of use, makes sure that much of the time Ranma is caught by just the wrong temperature of water at the wrong time. Being teenage is awkward enough...lucky he, uh ...or she, is a good fighter.
In one episode girl-Ranma gets pregnant!...Just kidding. Rumiko Takahashi wouldn't be that cruel.There are lots of other characters in the Ranma-verse, and every one of them is weird. Well maybe one or two exceptions, but most are weird, and many transform with the hot or cold water. But their changes have to do with their species, not gender. It can all be pretty confusing. You probably want to start with the first season Ranma1/2 TV series. The second season is called Ranma 1/2: Anything-Goes Martial Arts. The third season Ranma 1/2: Hard Battle. There is also an OAV series, and two movies. My favorite episode Ranma 1/2: Hard Battle, Dharma Chameleon (the name of the tape), I LOVE YOU! MY DEAR, DEAR, UKYO (the name of the episode).
This may all sound very slapstick, and it is, but there is lots of warmth to her Rumiko's work. Not every episode is excellent, but I've seen lots (not all mind you) and haven't seen a truly bad one yet.