The group formed in 2001, and major debut on March 22, 2006. The group originally consists of 6 members and the group name is from initial of their names: Kazuya Kamenashi (K), Jin Akanishi (A), Kouki Tanaka (T), Junnosuke Taguchi (T), Tatsuya Ueda (U), Yuuichi Nakamura (N). When Jun Akanishi left on July 2010, Kazuya Kamenashi's initial became KA. When Kouki Tanaka left on September 2013, Tatsuya Ueda's initial became TU. When Junnosuke Taguchi left on March 2016, Tatsuya Ueda's initial became T-TU.

Members

Kazuya Kamenashi (KA) - Born February 23, 1986, Blood type: B. Pink.

Tatsuya Ueda (T-TU) - Born October 4, 1983, Blood type: B. Blue.

Yuuichi Nakamaru (N) - Born September 4, 1983, Blood type: O. Purple.

Ex-members

Jin Akanishi (A) - Born July 4, 1984, Blood type: 0. Red. Left the group on July 2010 to solo debut.

Kouki Tanaka (T) - Born November 5, 1985, Blood type: B. Yellow. Left the group on September 2013 and is in INKT as KOKI the vocalist beginning October 1, 2014.

Junnosuke Taguchi (T) - Born November 29, 1985, Blood type: AB. Orange. Left the group on March 2016.

There are 32 singles out so far, among them Tragedy is used as Kindaichi Shounen no Jikenbo Returns 2nd Season OP2, 6 albums, 1 mini-album, and 2 best albums released.