Hmm.. can't really give a good summary... but it's supposed to be a really successful series in Japan. And one of the characters, Ruri, is supposed to be more popular than Ayanami Rei from Evangelion. Here's a link if you wanna know more about it~

This anime series is complete with 26 episodes, an OVA series called Gekiganger 3, and a movie called Prince of Darkness.