I thought this was coming. Yuuki Aoi will sing one of the songs on DECO*27's new album, Love Calendar, which is to come out July 25.
DECO*27 wrote and orchestrated two tracks on Ao-chan's album Petit Pas. At the time he said she added a lot to the songs, and he had thoughts about how he might orchestrate for her if they worked together again. He said he had been a fan of her voice-acting since Kurenai (2008). And she said that she had long been a fan of his work, too.
DECO*27 began his music career uploading tracks to NicoNico Douga, and only later got a commercial record contract. So perhaps he and Ao-chan are both otaku who have emerged from cyberspace into the larger world. On his blog, DECO*27 says that recently he has taken to going to bed at 1pm and getting up at 9pm, so he can work through the night.
The album describes a couple newly in love. The song Ao-chan will do is track 10, Kisou Honnou 帰想本能 ("An Instinct to Return"). DECO*27 describes the song as "cute but heart-breaking."
The album is available for pre-order from CDJapan, among other places. If you'd like to hear the song, here is a previous version featuring Hatsune Miku:
This is a song Ao-chan could really make something of. I can't wait.