Mikako Mihashi was born in 1965 near Sapporo city in Hokkaido, the north island of Japan.
In her teens she became active in the music sub-culture of Sapporo and participated as a support vocalist in the group P-Model.

She moved to Tokyo in her early twenties and published her first album Grace in 1990. Following this, she was a member of Sakata Akira's group Otemoto, and moved on to perform with the Haniwa All-Stars, under the leadership of the famous japanese percussionist, Kiyohiko Semba.

At the same time she was engaged in vocal improvisation projects including Sam Bennett's Third Person and John Zorn's Cobra. In 1993 she formed the new band ONI, publishing a first album Yomeiri in 1997. Concurrently she worked in collaboration with the shamisen player Tanaka Yumiko in the joint band Kitchen Drinkers, which is an experimental project attempting a new interpretation of traditional Japanese music.

In 1997 also, she perfomed as solo vocalist in the concert series Rock n' Kodo, in collaboration with the world reknowned traditional japanese drum group, Kodo. In 1998 ONI was disbanded in order to work full time on the newly formed group Sohonzan, whose approach is to infuse a strong mystical flavor into traditional japanese elements.

A more recent project is the duo Ringam, with japanese traditional Koto player Michiyo Yagi.

Mikako has also composed and perfomed music for numerous japanese TV commercials.