After the break-up of Number Girl, singer and songwriter Mukai Shuutoku decided to take an open approach to his next few projects.
He sound-proofed a basement and started Matsuri Studio, a place where he could write and record. Number Girl drummer Ahito Inazawa joined Mukai for some informal sessions, as Mukai acquired more equipment for his studio.
Mukai had previously used the moniker Zazen Boys on his work with pop singer hal and the band 54-71. He was billed under that name on a Rolling Stones tribute album.
At first, Mukai imagined Zazen Boys as a project on which guest musicians perform with him and Inazawa.
But in 2003, Mukai embarked on a series of solo tours dubbed "Mukai Shuutoku Acoustic + Electric". His sets included some spoken word pieces set to music. The wild abandon of his collaborative performances with hardcore band Panic Smile also left an impression.
Sensing a change in direction for Zazen Boys, Mukai decided to book the band for the Rising Sun Rock Festival. Now needing to flesh out the band's line-up, Mukai recruited Art-School bassist Hinata Hidekazu and Luminous Orange support guitarist Yoshikane Sou.
Hinata and Yoshikane joined Mukai in the studio to try out more material for Zazen Boys. By the end of 2003, Mukai Shuutoku had formed another band.
In 2004, Zazen Boys released two albums on Mukai's own independent label. The following year, Inazawa announced his departure from the band, citing creative differences. He has since formed Vola and the Oriental Machine.