It was started by actors in a theatrical company called "Otona Keikaku" (Project Adult) in 1995.
Its original members were Hakai (Sadao Abe), Boudou (Kankuro Kudo), and Baito Kun (Seminosuke Murasugi).
It was their longest album to date, at 27 tracks, and featured them covering a new variety of musical genres such as reggae and hip-hop.
[1] 2010 marks the group's 15th anniversary, and several releases and events are scheduled in honor of it, including a new album entitled 1!2!3!4!.
Several members of Group Tamashii also have jobs as actors and writers, in addition to their music careers.