Big cast. Good cast. Some experienced names. Some unusual names.
Here is a characters/seiyuus page, with pics of 18 characters and their seiyuus, and some info about the seiyuus.
The big name, of course, is Tanaka Rie. But Imai Asami, Asumi Kana, Satou Rina, Ueda Kana, Horie Yui, Kitamura Eri, Ogura Yui (an idol with at least one good seiyuu voice) and her singing partner Ishihara Kaori (a top young seiyuu) -- lots of good seiyuus. Sakai Kanako back from TV work. Kanai Mika, Takahashi Chiaki. Nao, who does the OP and was formerly in fripSide. And finally Neeko, who was Reborn in
Hitman Reborn, but is basically a (31-year-old) fashion model and singer with a somewhat wild style (especially for Japan): she appears to have a stud in her tongue....