There's also a manga, which was made before the anime, in Asuka comics. It's supposed to be released by Tokyopop by next spring, the last I heard. ^_^ I think I'm going to actually buy them, too.
The story is about a boy named Daisuke [14 years old], who has a huge crush on a girl named Risa. Risa rejects the poor guy before he even gives the girl a love letter [XP]. So, blah blah blah he's heartbroken blah blah blah and THEN he finds out that his family [which has a bit of a magic background, methinks] and all the men in his family took on the form of a man called Dark Mousy at age fourteen. [which I will mention is a very fine man.]

And then you can add in some humor and a cute 14-year old genious trying to capture Dark and you've got this anime.