Ranma 1/2 is the title of the manga series by Rumiko Takahashi and the animated seies based on it. The story follows the comic problems of 16 year old martial artist in training, Ranma Saotome, a victim of a strange cursed pool --- whenever he's splashed by cold water he turns into a red-head (and incredibly well-built) young female. Hot water reverses the spell. It could be worse, becase his father turns into a gigantic but lazy panda when he gets wet. His father has arranged a marriage for Ranma with the daughter of a fellow martial artist. Akane Tendo is a martial artist in training herself and hates boys. For Ranma and Akane, it's hate at first sight.
Throw in lots of other strange characters and the things get even more interesting. There's Kuno, head bully of the highschool who leaves Akane, but falls in love with the female Ranma. Then there's Ryoga who followed Ranma since junior high because of a grudge (he's in love with Akane and wants to kill Ranma, and also fell into a cursed pool and turns into a piglet. Akane, not realizing this is the transformed Ryoga, adopts the cute little piggie and named it P-chan. Ranma is honourbound not to reveal Ryoga's secret, much as he would like to). Then there's Shampoo, another martial artist from China. She was defeated by Ranma in both forms --- where she comes from, the rules are: If you're defeated by a man, you must marry him. If you're defeated by a woman, you must kill her. --- Oh ya.. and she also fell into on of those cursed pools and turns into a kitty when she gets wet (Guess which animal Ranma is phobic about??)...

This isn't a love triangle... it just makes things really interesting this way. Is it very silly? Yes. Is the humour low-brow with lots of slapstick and gratitious nudity? Uh huh. Is it addictive? Hell yea!
Ranma 1/2 is one of the most popular series and manga currently in Japan and is rapidly becoming on of the biggest anime hits in the US.

- Ranma Saotome -
It's not easy being a teenaged martial artist... but it's even worse when your martial artist father, Genma, takes you from home at an early age to go on a decade-long training mission in China. He doesn't speak a word of Chinese, and yet he insists on bringing you to the cursed training grounds known as Jusenkyo, where falling into one of many springs instantly turns you into whoever or whatever drowned there last. And then, the two of you have this little accident...

...From now on... a splash of cold water will turn your father into a giant panda, while you... well, you turn into a red-haired (and incredibly well-built) female version of yourself. Hot water will reverse the effect, but only until the next time. What's a half-guy, half-girl to do??