In 2005, W starred in their first musical, Mysterious Girl Detectives Cara & Mel: The Case of the Stolen Dangerous Violin (2005).

W was scheduled to make a comeback in 2007, but after media reports of Kago dating and smoking again surfaced, her contracted was terminated and Up-Front Promotion announced that W had disbanded.

In 2004, W's formation was announced not long after Nozomi Tsuji and Ai Kago's graduations from Morning Musume.

Tsuji and Kago had previously worked together in one of Morning Musume's sub-units, Mini Moni, as a side project.

[2] W released their debut three-song EP, Koi no Vacance, the title track being a cover version of The Peanuts' 1960 song.

On January 11, 2006, the release of a new single, "Dō ni mo Tomaranai" on February 22, followed by their third full-length album, W3: Faithful on March 15, was announced.

In January 2007, Kago returned to Tokyo and did assorted clerical work at her agency's office while the company was making preparations for her comeback.

Not long after, photographs of Kago smoking underage for a third time, as well as going on a "dirty weekend trip" to an onsen with a 37-year-old man, began circulating in the media, completely tarnishing her reputation.

Project's 20th anniversary summer concert, leading to both their names trending on Twitter; they were scheduled to perform together, but Tsuji dropped out from maternity leave.

Project's spring concert and were releasing their previously cancelled works, "Do ni mo Tomaranai" and W3: Faithful, on March 30 as digital releases; "Do ni mo Tomaranai" would be bundled as a double A-side single with "Choi Waru Devil.

Project's spring concert, the two performed together in front of a crowd of 5,000 people for the first time in 13 years.