Ranma 1/2 [Manga]

Ranma Saotome (and others) is cursed to turn into a girl (or other animals, depending which cursed pool they fell in) when splashed with cold water. The only way to temporarily reverse the curse is to get splashed with hot water. Mix in the fact that Ranma is a (unlucky) martial artist and hates when others look at him as weak due to the curse, trouble and rowdiness ensues, naturally.