Miharu Koshi was born in Tokyo. Her parents were both working classical musicians with strong connections to a number of contemporary classical composers. From an early age Miharu studied piano under the tuition of Ms Emiko Iimori. In those years, Miharu’s parents preferred that she study piano playing rather than composition. She also undertook vocal training under Ms Hiroko Asaoka, as well as studying ballet and jazz dance choreography under the tuition of Katsuhiko Hoshi. Learning these techniques gave the teenage Miharu a keen interest in chanson, jazz and classical music's, rather than the four-four rock and roll beats favoured by most teenagers.
By 1978 Miharu had began recording her own ‘chansonesque’ compositions and between 1978 and 1982, she had a number of hits in the contemporary Japanese popular music style then known as ‘new music’. By 1983 Miharu had developed a considerable interest in the use of multitrack recording techniques, as well as recognising the opportunities for composition then opening up through the use of pre programmed electronic instruments, such as those being pioneered by artists like Japan’s Yellow Magic Orchestra (YMO), Germany’s Kraftwerk and the Belgian band Telex. This lead to her joining the seminal Japanese technopop label ‘Yen records’, where she began collaborating with former YMO leader and texhnopop music pioneer Haruomi Hosono.
In 1984 she recorded her first LP (Tutu) in this new vein. The LP included a cover version of the Telex hit ‘L’Amour Toujours, which was recorded in Brussels and where Miharu was backed by members of the Belgian band. The LP was produced by Hosono. Her next LP ‘Parallelism’ (1984) also appeared on Yen records, and included a stunning technopop cover version of the chanson ‘in the forest of Saint Germain’, first recorded by french chanteuse ‘Barbara’. Again the LP was produced by Hosono and he also shared credits for composition and instrumentation. During this period, the success of Miharu’s first two LP’s lead to them being leased by Dutch label ‘Pick up’ records, and to her receiving her first exposure outside of Japan, as well as to her undertaking a short European tour.

After the demise of Yen records, Miharu was invited to join Hosono’s new label ‘Non Standard’ records, where her labelmates included both World Standard and the Pizzicato V as well of course, as Hosono. Her third technopop LP appeared in 1985 and was entitled ‘Boy Soprano’ It was on this LP that Miharu first allowed her classical arrangement skills full reign on songs such as a cover version of Shuberts ‘Ave Maria’, giving well known melodies a new lease of life through her lush techno arrangements. During this period Miharu also began to play a crucial role in Hosono’s new solo project FOE (Friends of Earth), where she worked as both a keyboard player and arranger. This also lead to her appearing with FOE on a number of dates in New York in 1986.

In 1987 Miharu released her first LP of cover versions entitled “Echo de Miharu’, where she rearranged and rerecorded versions of popular 1930’s and 1940’s film songs and songs from broadway shows and musicals. Her choice of repertoire for this ambitious project included: Satricon, It’s raining sunbeams, diga diga do, how much is that doggie in the window? etc

Following on from this, Miharu’s next CD (Passpied) again featured more cover versions of popular favourites from generations past, this time using amongst others the work of 1940’s US composer Leroy Anderson as a reference, with electronic cover versions of some of his most well known compositions such as ‘Syncopated Clock’, ‘Belle of the Ball’, Typewriter etc. Toward the end of the 1980’s, Miharu made her acting debut, as well as breaking into new musical areas such as music for films, theatre, and TV commercial music. In 1989 she also received the ‘10th Advertisement Company Award for Composition’ for her music used on a popular Japanese TV commercial.
In 1990 she released her first CD book entitled ‘shinzo no ue’ (above the heart) where alongside her writings, the accompanying CD featured several short ‘well known’ classical piano and vocal pieces reworked into her own unique style. This was followed in 1991 by another album length CD, this time featuring all her own compositions. The CD entitled ‘Chichi to Pistoru’ (father and the gun) featured several collaborations with composer Kouji Ueno, and the music itself explored a hitherto unknown ‘darkerside’ to Koshi’s work. As promotion for this CD Miharu also undertook a short Japan wide tour, where she received ecstatic reviews as a result of the elaborate stage sets and choreography which she based her live performances around.

Following on from this, Miharu’s 1992 release ‘source d’ espoir’ looked at combining the styles of Miharu’s favourite composers against the burgeoning rave/dance music culture. She also released a second CD in 1992, entitled ‘La Voix de Paris’ (the voice of Paris), where she reworked a number of early 20th century chansons by French composers such as Poulenc, Milhaud and Francaix into her own unique style. Concentrating on this particular vein, Miharu followed this up with her 1995 CD ‘Chanson Solaire’ , which once again covered assorted works from Miharu's favourite composers.

In 1996 Miharu officially renewed her acquaintance with former ally Haruomi Hosono on a new project titled ‘Swing Slow’. For this concept the duo aim was to synthetically recreate the music's of the 1940’s, this time concentrating on such celebrated US balladeers as ‘Les Paul and Mary Ford’. Although Miharu herself feels in hindsight, that this was not the strongest of her works, the CD received very positive reviews, and bought Miharu’s arrangements, vocals and keyboard skills further acclaim outside Japan. The success of Swing Slow was followed in 1997 by the release of Miharu’s next solo CD entitled ‘Rodeo de Paris’.
Between 1997 and 2000 Miharu returned to composing music for films, TV commercials and theatre, as well as undertaking arrangements for a number of artists (including composer Toru Takemitsu) and in 2000 followed up her three year absence by signing to Daisy World records, and releasing a new CD titled 'L’Assassinat de la rue Pelican’ (the assassination on pelican street). This was followed in 2001 by her second CD for Daisy World titled 'Frou-Frou', which was again based around Miharu’s outstanding ability to breath new life into classic hits from the 1930s and 1940’s.

In 2003, Miharu appeared in the marionette drama “Hans the hedgehog” produced by the Youkiza theatre company. She also wrote and produced its musical score. In March 2003 she released her new album “Corset” and gave her “Musique-hall - Corset” live performances. In November “Musique-hall” received it European debut at the Berlin Jazz Festival. Miharu appeared by special invitation and the performance received very favourable reviews. In 2004 Miharu performed at Tokyo's Ohji Hall in the event “Royal Apron”, with trio of piano, accordion and fagott. In July 2005 she gave her debut performance of “Musique-hall - Les Judas” at Tokyo's Artsphere space.

In 2006 Miharu wrote and recorded the music for NHK TV's animation “Birdie - the small plane of the southern islands”. In 2007 she contributed soundtrack music to the animated film “EX MACHINA”. That year she also participated in the live performances of HASYMO's Haruomi Hosono, as a member of his World Shyness orchestra, as well as contributing accordion to his solo album titled; "Flying Saucer 1947". In August 2008 Miharu released her original album “Les Judas” and performed “Musique-hall - Les Judas” at Tokyo's New National Theatre.

In 2011 Miharu organized and performed the vintage themed live called “Chanson epidemic”. Performed with vocal and piano in the style of French composers; Charles Trenet, Jean Sablon, Yves Montand, Andre Clavaeu. The time she considers to have been the most beautiful of French chanson. Following on, in 2012 Miharu organized the solo live event “Evening Café – dedicated to her mother” where she performed songs of French Chanson and 1930s French ‘Hot Jazz’. In 2013 Miharu's latest CD “Madame Crooner” was released. This work showcased songs made famous by Miharu’s favorite crooners from the 1920s and 1930s. In July 2013 she performed in concert in Tokyo with Fabian Reza Pane on piano, Motoya Hamaguchi on percussion and Hitoshi Watanabe on bass