Ranma 1/2 (らんま 1/2). The story of a boy who turns into... a girl!
[Introduction to the series; Fan section; Rings]
Ranma 1/2 was created by Rumiko Takahashi
This is the story of a boy, named Ranma Saotome (早乙女 乱馬). He is 16 years old, and (like many characters in the series) a martial artist. As part of his training, his father Genma (玄馬) took Ranma on a decade-long training trip to China. During this trip, father and son visited a place called Jusenkyo, where falling into one of the many springs causes you to turn into whatever drowned there last every time you get hit by cold water; the effect can temporarily be reversed using hot water. Both had a little accident, so, from this moment on, Genma changes into a panda, and Ranma changes into a gorgeous, red-haired female version of himself.
Genma has a friend, Souun Tendou (天道 早雲), who has three daughters: Akane (あかね), Nabiki (なびき) and Kasumi (かすみ). Souun is the owner of the Tendou Doujou (天道 道場), (doujou means "training hall") and Genma promised him that Ranma would marry one of his daughters, so the future of the doujou would be guaranteed. As soon as the Tendou family found out about the Jusenkyo curse, Akane, the youngest and most tomboyish one, was promptly nominated by her sisters for the honor of being Ranma's fiancee. 
Akane and Ranma don't agree, of course since Ranma wants a cure rather than an engagement to some uncute (in my opinion she isn't THAT bad) tomboy and Akane simply hates boys. But yet they still love each other (though they don't seem to very often) and both are very jealous.
Akane isn't Ranma's only fiancee. Somewhere in China, Ranma meets a really cute Amazon girl: Shampoo (シャンプー), one of my favs ^_^. Telling the whole story is taking too long, but Ranma beat Shampoo in a fight and an Amazon law says that an Amazon has to marry the man who beat her. Shampoo is really fond of Ranma and extremely tenacious. One little detail: Shampoo is cursed too and therefore she changes into a cat. And since Genma trained Ranma throwing him into a pit full of hungry cats, he's deadly afraid of them...
Trouble doesn't stop here. Genma has a strange nature and committed many "crimes" that Ranma suffers from. An example is Ranma's engagement to Ukyou Kuonji (右京), also one of my favs. This cutie bakes okonomiyaki (some kind of pizza) all the time. Her father had an okonomiyaki cart and Genma (slave of his stomach) traded Ranma's (he was a little kid back then) engagement for the cart. But then they had a problem and Ukyou was dumped. Ukyou couldn't bear the shame and posed as a man (her name is a guy's name) until she met Ranma again, to take her revenge. Her feelings changed drastically though when Ranma called her "cute" and since then, he had his third fiancee...
These are just a few examples of the romantic triangles that appear in the series. Akane is popular as well (most tenacious guy is Ryouga (良牙), who changes into a pig (P-chan) which is Akane's pet), and Ranma even attracts guys in his female form ^o^. This is one of the things that I like in the series. There's also lots of martial arts, action and loads of form/gender changing fun, which sometimes make the series somewhat ecchi (having sexual content), but this only adds to the fun. But it's not only humour, some dramatic parts can make you cry as well. I can recommend this to everyone older than 12 years, since the stories are really good and also very addictive. I'm hooked too ^_^!
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