御祭騒ぎ(Omatsuri Sawagi / Festival Uproar) is the sixth doujin album by PolyphonicBranch. It was released at THE VOC@LOID M@STER 16. It features the vocals of GUMI and Miku and one track sung by an utaite.
The CD comes with a 12 page booklet with illustrations.
It can be ordered from Amazon.