W (ダブルユー, Daburuyū^?), also written as Double You or Double U, was a Japanese pop duo associated with Hello! Project. Nozomi Tsuji and Ai Kago, former fourth generation members of Morning Musume, were in the group.

W's formation was announced not long after the "graduation" of Kago and Tsuji from Morning Musume was announced in early 2004. At the time, the duo—longtime best friends since they met at the auditions that landed them in Morning Musume in 2000—were simultaneously in both Morning Musume and one of its most popular subgroups (or side projects), Mini Moni. The latter group was about to be disbanded with the departure of Mika Todd (see Mini Moni's entry for details); with Kago and Tsuji almost at a complete loose end, the decision to pair the two best friends and lifelong bandmates together in a new group was made almost immediately.

As they were winding down their Mini Moni and Morning Musume duties, W released their debut three-song EP, Koi no Vacance, the title track being a rocked-up cover version of a 1960's hit by Showa period female duo The Peanuts. The EP was followed a few weeks later by their debut album as W, Duo U&U, which contained covers of other Showa period female duo songs exclusively. One of the other groups covered by W on the first album was Pink Lady, a 70's-era duo that was becoming active again as a performing (if not recording unit). Since Kago and Tsuji had done two Pink Lady songs ("Southpaw" and "Nagisa no Sinbad") on Duo U&U, Pink Lady were invited to perform with W on Japanese television as a one-time four-piece ensemble. Their joint performance of "Southpaw" became a trading favorite amongst American Hello! Project fans on VCD, DVD, and BitTorrent (Pink Lady also sat in with Kago, Tsuji, and their Morning Musume bandmates on "Nagisa no Sinbad" and a medley of the former act's "S.O.S." and the latter's "Love Machine" on the same show).

A group is a number of things or persons being in some relation to one another.

Chemistry

Biology

Cosmology

Other