Jimsaku is a bass-and-drums duo formed in 1990 by Tetsuo Sakurai and Akira Jimbo, both formerly of Casiopea. In 1989, the two had formed a separate side project, Shambara, with other musicians. When Casiopea guitarist Issei Noro demanded Shambara's dissolution, Sakurai and Jimbo refused and left Casiopea instead, wanting to return to an instrumental-band format — a departure that, according to Wikipedia, ended the original Casiopea lineup entirely rather than being a side-project footnote.

Their name is a portmanteau of Jimbo and Sakurai. Their early work drew heavily on Latin and Samba rhythm, traced directly to a trip Sakurai took to Brazil in the early 1980s — a real stylistic departure from the mainstream Japanese fusion sound both men had just left, which stayed popular in its own right. They kept up a punishing release schedule through the mid-1990s, at points releasing two albums a year, until the pace forced them to abandon the Latin influence in favor of a harder, drum-and-bass-heavy sound.

They played their final show under the Jimsaku name in February 1998, announcing the split during the concert itself. The breakup held for two decades. In 2019 they reunited at Akira Jimbo's 60th birthday celebration and kept performing, culminating in a new album, Jimsaku Beyond, in 2021. Both members now also play together with former Casiopea keyboardist Minoru Mukaiya in a group called the Katsushika Trio, formed 2021/2022 and initially focused on revisiting 1980s Casiopea material.

Jimsaku's sound moved across three distinct phases: Latin/Samba-influenced fusion in their earliest years (drawn from Sakurai's time in Brazil), a harder, more conventional fusion sound through the mid-1990s, and finally a drum-and-bass-heavy direction that led directly to the group's 1998 breakup.