Miku Hatsune from "Vocaloid 2" a virtual singing game. Basically, you type in the lyrics in Kanji, add a melody, and the software does the rest. I find it very, very addictive~ and Miku is adorable. 8D

You can listen to a demo song here; http://www.crypton.co.jp/download/demosong/extra/CV01_02_kakurenbo.mp3

*EDIT
More demo songs~

http://www.crypton.co.jp/download/demosong/extra/CV01_01_ballade.mp3

http://www.crypton.co.jp/download/demosong/extra/CV01_03_pops.mp3