10-nin Matsuri

The Hello! Project shuffle units (シャッフルユニット, shaffuru yunitto^?) were an annual event in the Japanese idol collective Hello! Project that started in 2000. The idea was to shuffle up the existing Hello! Project groups and soloists (e.g. Morning Musume, Country Musume, Aya Matsuura, Melon Kinenbi, and others) into one of three groups for a season-long collaboration to see which shuffle group can sell the most singles.

Each year's shuffle had a common theme: 2000's shuffle group theme, for example, was color and the groups were Akagumi (red) 4, Kiiro (yellow) 5, and Aoiro (blue) 7. Despite the commonality in theme and same B-side song, each group tends to sing a different style A-side song (details below).

Eventually, this became more of a tradition than a competition to outsell. In 2003 the three groups' songs were merged and sold as one single/mini-album. In the fall of 2004, only one unit was formed: The Hello! Project All-Stars, a collaboration of all 46 contemporary Hello! Project members to perform "All for One and One for All!".

The three shuffle units continued in 2005 with Sexy Otonajan (セクシーオトナジャン, Sekushii Otonajan^?), Puri Puri Pink (プリプリピンク, Puripuri Pinku^?), and Elegies (エレジーズ, Erejiizu^?). Unlike previous years, the majority of Hello! Project did not participate in 2005's shuffles (each of the three groups had 3 or 4 singers.) The 2005 shuffle units were also the first ones that ex-Morning Musume members participated in.

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Wikipedia