This anime was enjoyable to me at some points, but there were really times where i just wanted to get up and walk away.
If you don't have the right determination (or laziness) this show could lose its stuff really fast.
Its about a fourteen year old named Niwa Daisuke who, on his fourteenth birthday, finds out that members of the Niwa bloodline have been, for years, transforming into a thief named Kaitou Dark (or dark mousey, w.e.). It happens to him all of a sudden while he's thinking of his crush, Harade Risa. Its then explained to him the whole Niwa situation and the trigger for his transformation is directly related to the heart. In short, whenever he thinks about Risa, he turns into dark.
There is also a family like the Niwas called the Hikaris, who are actually the sworn rivals to the Niwas. The Hikari boy like Daisuke is named Satoshi, who goes to Daisuke's school under the name of Hiwatari Satoshi. Like, Daisuke, a being like Dark exists inside him known as Krad. Krad doesn't come out when Hiwatari's heart is stimulated though, nope, Krad forces his way out of Satoshi.
The whole routine for the first 13 episodes or so is basically the same, dark steals something, plus a little side mission. Dark steals something, plus a little side mission.
The fun comes back into the series when an American named Hio Mio transfers into Daisuke's school and from that point on, the series is basically addictive.
For your sake of knowing, Risa has a twin sister named Riku who differs from Risa in every aspect but her face.
Good show, though standing back and looking at it, it could be considered shojo. I'll give it an 8.