Fumio Itabashi (板橋文夫) was born on March 8, 1949, in Ashikaga, a city in Tochigi Prefecture that sits on the Watarase River, the water that would later give his best-known piece its name. He began playing piano at eight and went through the high school attached to the Kunitachi College of Music in Tokyo and then the college itself. Japanese profile pages say he turned to jazz after hearing a senior student at Kunitachi, the pianist Takehiro Honda, play, and that he was already performing while still a student. The saxophonist Koichi Matsukaze, who entered Kunitachi in 1968, is described in his profile as playing in a bass-less trio with Itabashi and Shunji Tsuda in his second year there.

Those same profiles date his professional start to 1970, in the quintet of Sadao Watanabe. The earliest record credit that can be checked is Watanabe's 1972 album for CBS/Sony, recorded at Iino Hall in Tokyo on February 24, 1972, with Itabashi on piano and electric piano, Masayuki Takayanagi on guitar and Hiroshi Fukumura on trombone. A 1973 date with Kohsuke Mine's quintet (Daguri, Victor, recorded June 21 and 25, 1973) followed, and in October 1974 he played piano on the guitarist Kazumi Watanabe's Monday Blues (RCA, released 1976). On January 15, 1975, at PSC Recording Studio in Tokyo he was the pianist on Terumasa Hino's Speak to Loneliness for East Wind, with Tsutomu Okada on bass, Motohiko Hino on drums and Hideo Miyata on tenor and soprano saxophones.

His own trio was recording by then. On April 26, 1975, at the Tokyo club Aketa's, he cut the long live set that appeared two years later as Rise and Shine, with Takeharu Hayakawa on bass and Kenichi Kameyama on drums. On March 1, 1976, at Daichi Seimei Hall in Tokyo, the trio of Itabashi, the bassist Tsutomu Okada and the drummer Takuji Kusumoto recorded Toh (濤) live for the Frasco label: three pieces, among them "Alligator Dance" and "Good-Bye," two compositions he has returned to for decades.

In 1977 he took the piano chair in the quartet of the drummer Takeo Moriyama, and the band's debut, Flush Up, was recorded live at Shinjuku Pit Inn on March 1 and 2, 1977, with Hideaki Mochizuki on bass and Tomoki Takahashi on tenor and soprano saxophones. He stayed for Hush-A-Bye (1978) and Smile, recorded November 10 to 12, 1980, where Matsukaze guested and the second piece on the first side was Itabashi's own "Watarase." The Moriyama connection lasted: he is on that band's Live at Lovely (1991) and on two 1994 albums, and in 2016 the two recorded a duo album of Japanese children's songs for Pit Inn Music.

As a leader he made Nature for Nippon Columbia's Better Days label on March 13 to 15, 1979, a session with vibraphone and soprano saxophone alongside the rhythm section, classified on Discogs as post-bop and modal. Then came the record that carries his name abroad. On October 12 and 13, 1981, at Nippon Columbia's 1st Studio in Tokyo, he recorded Watarase alone at the piano, digitally, for the Denon label; it came out on February 25, 1982. Its seven tracks mix two standards ("Someday My Prince Will Come" and "I Can't Get Started"), a reading of Abdullah Ibrahim's "Msunduza" and his own pieces, the title tune among them. It was never widely available outside Japan until Wewantsounds reissued it on April 5, 2024.

The rest of the 1980s ran on larger ensembles and touring. Impact (1984, Paddle Wheel) is an arranger's album, credited with a horn section, guitar, synthesizer and three different drummers, and Red Apple (recorded December 10, 1985, released 1986) added Kazutoki Umezu's alto saxophone to his trio. To Be (Denon, recorded April 18 to 20, 1989) was a trio-plus-percussion set with Nobuyoshi Ino on bass that introduced "Gospel '89." Japanese profiles say he toured the world as a sideman with the drummer Elvin Jones and the trombonist Ray Anderson; the record evidence is Trust in Blue, Akira Ohmori's 1988 Denon album billed "meets Elvin Jones," on which Itabashi plays piano with Jones and the bassist Yoshio Suzuki, and Anderson's Wishbone, recorded in December 1990 at Clinton Studios in New York, on which he plays piano.

In 1992 he began issuing records on his own imprint, Mix Dynamite, which is also the name of his working band. The early catalogue numbers include a Fukuoka gallery recording with the percussionist Tomohiro Yahiro (October 3, 1992), the live album Saiyuki, recorded at Shinjuku Pit Inn on November 3, 1992, and Tsuki no Tsubo (1993), recorded at Yugawara with the Korean haegum player Kim Sung A, the percussionist Lee Tae Baek, the koto player Kazue Sawai and the bassist Tetsu Saitoh. Film work reached Taiwan: a soundtrack album, The Red Lotus Society, was issued there in 1994, and Japanese sources list the Taiwanese production Peach Blossom Land (暗恋桃花源) among his scores. Folk song became a second thread: his 1997 album Otsukisama uses Okinawan songs and has the Yaeyama singer Tetsuhiro Daiku on three tracks. The Mix Dynamite Yu (1995, Omagatoki) is the band album, with Ino, the drummer Shota Koyama and the saxophonist Hiroaki Katayama.

Travel marks the 2000s as much as bandstands do. North Wind is a solo double CD recorded live in Kitami, Hokkaido, on March 4, 1998; Jumbo! Obrigado! (2001) is a two-disc set titled for Nairobi and the Seychelles, made with Nobuyoshi Ino, Koyama, the percussionist Akira Ishikawa and the Kenyan group Ensemble Wakenya; Unicorn (2000) joins him with Korean musicians and Sawai. On June 8, 2011, he played Watarase at Watarase outdoors on the riverbed itself, issued that October. From 2010 he led the trio FIT! with the bassist Takashi Seo and the drummer Yasuhiro Takemura, and he leads a jazz orchestra whose album Fumio69 Rock & Ballade appeared in 2018. His score credits include Wakamatsu Koji's film 11.25 Jiketsu no Hi: Mishima Yukio to Wakamono-tachi, whose soundtrack was released in 2012, and Japanese sources list Yanagimachi Mitsuo's 19-sai no Chizu among his earlier work.

The Watarase piece has had a long second life. The Sapporo producer Kuniyuki Takahashi and the German producer Henrik Schwarz made remixes released on Studio Mule in March 2021, and Joe Claussell remixed it in 2022. A symphonic poem version for piano, folk song and orchestra was recorded with the Kanagawa Philharmonic, P-Vine issued Watarase -Echo- in 2024, a six-version set called Watarase "Voice" in January 2025 and the orchestral Watarase Symphony on vinyl on July 8, 2026. Itabashi turned 77 in March 2026, and on February 4, 2026, he played a duo concert with Seo at Live Spot RAG in Kyoto. He has also taught: according to her own biography, the pianist Satoko Fujii studied jazz in Tokyo with him as a young adult.

His piano is physical and fast. A Kyoto live-music venue's biography of him describes fast, aggressive playing with chopper-style and glissando techniques, and the titles and track lengths of the Pit Inn and Aketa's recordings bear it out: single pieces of 20 and 30 minutes, built on long modal vamps and bursts of free playing. Nature is filed by Discogs under post-bop and modal jazz, The Mix Dynamite Yu under free jazz and jazz-funk, and the Nairobi recording under avant-garde jazz and Afrobeat, which is a fair map of the territory he covers.

The second strand is song. "Watarase" works like a folk tune, a theme short enough to be sung that he has stretched, shrunk, orchestrated and handed to remixers, and the same ear leads him to Okinawan songs, Japanese children's songs on the Moriyama duo album, and Korean and Kenyan collaborators. The one influence named in his biographies is Honda, whose playing he heard at Kunitachi. His discography also reaches film music and house-music remixes of his tunes, but the core of it, from the 1976 trio live album to the 2023 Tohtou sessions, is improvised jazz.