There's an "18+" game called "to.." going on sale 10/31.
official page is http://www.marigold.co.jp/to/

The OP is sung by Sakakibara Yui (a.k.a. Hinano Mayo), and there's
a downloadable MP3 of it on the web page (full song).

Yui is doing a voice too.

to.. [Windows]
 Ogasawara Miho    :: Sakakibara Yui
 Kitazawa Mari     :: Isshoku Hikaru
 Mimura Satomi     :: Sakurakawa Mio
 Saeki Youko       :: Kaori
 Shiraishi Kyouko  :: Nagasaki Minami
 Mimura Tomoki     :: unannounced

--
Hitoshi Doi (LaLaLu FC #49, Cutie Pai FC #2)
                           " this space for rent "
http://www.usagi.org/~doi/                                    doi@usagi.org