An anime, in where Niwa Daisuke turns into the kaitou Dark at age 14, as does every male Niwa. Daisuke transforms into Dark when he ('basically') sees his crush, Risa. Daisuke will remain having Dark as an Alter Ego until he can get Risa to like him back. That might be a while, considering that Risa likes only one person - Dark. Risa's twin sister, Riku, likes Daisuke.
Now, because Dark is a thief, (hence the 'kaitou Dark' as his nickname) the police are always out to get him, especially Hiwatari Satoshi. Satoshi is a genius boy who is in Daisuke's class. He seems to know more about Dark and Daisuke than he lets on, though...
Although the anime is much worse than the manga, this anime is very easy to like. The name might be odd, but it'll make sense after a while. At least you can't mispronounce it.
D.N. Angel is an anime. Anime is typically cool.