Ranma ½

Ranma ½ is a martial arts romance/comedy anime, based on a manga by Rumiko Takahashi. Thanks to his idiot father, 16 year old martial artist Ranma Saotome is cursed to turn into a girl whenever he's splashed with cold water; hot water will turn him back to a boy, but only until the next time he encounters cold water. Soon after he's cursed, he finds out his father also engaged him to a girl he's never met, much less heard of, and she isn't any happier about this "surprise" than he is.

And so begins the story.