Mikio Masuda (益田幹夫, Masuda Mikio in Japanese order), who was also billed as Mickey Masuda, was born in Osaka on 14 August 1949. According to his record company biography, he was drawn to modern jazz at 16 and took up the bass, switched to piano a year later and began working professionally, and at 19 moved to Tokyo, where he became a studio musician and sat in with a long list of bands. He had left the high school attached to Kwansei Gakuin University without graduating.

The earliest recording credit that can be documented is Terumasa Hino's sextet LP Fuji, cut at Victor Studio on 8 March 1972, where Masuda plays electric piano beside the guitarist Kiyoshi Sugimoto, the tenor saxophonist Takao Uematsu, the bassist Yoshio Ikeda and Hino's brother Motohiko Hino on drums. His official biography dates his entry into Hino's quintet to that year. On 28 August 1972 he was the pianist on the first record led by the trumpeter Shunzo Ohno, Falter Out, and in November and December 1972 he played on the Tokyo sessions of the American singer Johnny Hartman, issued as Hartman Meets Hino, with Hino on trumpet, and, in part, Hartman Sings Trane's Favorites.

The Hino group took him to Europe in 1973. The 2016 box set from the International New Jazz Meeting at Altena Castle in West Germany, held on 23 and 24 June 1973, has him on piano beside Hino on "Akubai" and "Rock for Altena". On 29 June 1973 the quintet, with Ikeda, Motohiko Hino and the conga player Yuji Imamura, was recorded live at the Domicile club in Munich for the German label Enja as Taro's Mood. Back in Tokyo he plays piano on Hino's CBS/Sony albums Journey into My Mind (recorded 19 and 20 December 1973) and the double LP Into Eternity (28 May to 1 June 1974), the second of which includes two of his own pieces, "Song for Bumiji" and the solo "Mickey's Trip".

His first record as a leader, Trace (East Wind, 1974), was recorded at Victor Studio on 9 and 12 June 1974 with Hino on flugelhorn for one track, Uematsu on tenor saxophone, Hideo Miyata on flute, Tsutomu Okada on bass and Motohiko Hino on drums. Four of its six pieces are Masuda's own. The two Hino pieces are "Black Daffodils" and "Alone, Alone and Alone"; the first shares its title with the comeback album Masuda would release in 1997. His record company biography says he joined Art Blakey's Jazz Messengers in 1975, and Japanese biographies place a stay in the United States in 1974 or 1975; no Jazz Messengers recording credit for him has surfaced, so that period is known from biographical accounts rather than from a record sleeve.

In the middle of the decade he became a regular in the Tokyo fusion bands. On 20 July 1975 he was on keyboards for the Motohiko Hino Quartet's live LP Toko, recorded at Nemu no Sato with Kazumi Watanabe on guitar and Isao Suzuki on bass, and he wrote its opening piece, "You Make Me So Sad". The tenor and soprano saxophonist Kohsuke Mine used him on the live quartet LP Solid (Yamaha Hall, 29 October 1975, Fender Rhodes and organ) and on Sunshower (9 and 10 February 1976, clavinet, organ and synthesizer). In January 1976 he joined the alto saxophonist Hidefumi Toki's quartet for Sky View (Frasco), billed "Featuring Mikio Masuda" and including his tune "Let's Get Together".

Mickey's Mouth (East Wind, 1976), recorded in April and June 1976, is the album where he is the main voice: Fender Rhodes, clavinet, Yamaha organ, Mini Korg and ARP String Ensemble, with Mine on soprano saxophone, the guitarist Masayoshi Saitoh, the bassist Osamu Kawakami, the drummer Arihide Kurata and the percussionist Guilherme Franco. "Let's Get Together" turned out to be his signature piece. It is on Mickey's Mouth, on Sky View, on a 1977 NHK radio transcription set shared with Mine and Sadao Watanabe, on Moon Stone (1978) and on Corazón (1979). The sideman dates of 1977 include Takao Uematsu's Straight Ahead (12 October 1977), the singer Yasuda Minami's Moritat (29 and 30 December 1977, with Mine on tenor), the festival double Jazz of Japan Live Under the Sky '77 (24 July 1977, Denen Colosseum, Tokyo), where he plays electric piano on two tracks, and Hino's Hip Seagull, recorded in Tokyo in August 1977 and in New York that December, whose credits include the guitarist John Scofield, the vocalist Kimiko Kasai, the drummer George Otsuka and Mine.

Moon Stone (Better Days, recorded 1 to 3 December 1977 at Nippon Columbia's first studio) was produced by Masuda himself, with Kazumi Watanabe and Kazumasa Akiyama on guitars, Motohiko Hamase on bass and Hideo Yamaki on drums. His official biography places his joining the Sadao Watanabe quintet in 1978. The same year brought the first of two New York recordings for the Electric Bird label. Corazón was cut at Electric Lady Studios between 11 and 18 November 1978 with the drummer Bernard Purdie, the bassist Anthony Jackson, the percussionist Sammy Figueroa and a string section arranged and conducted by Dave Matthews; it takes in Carole King's title song, Lee Oskar's "Before the Rain" and Sadao Watanabe's "Samba Em Praia". Goin' Away followed at A&R Recording on 9 to 14 July 1979, arranged by Bob Freedman, with Michael Brecker on tenor saxophone, the bassist Will Lee and the guitarists Georg Wadenius and John Tropea.

Between the two New York trips he played electric piano on three tracks of Kazumi Watanabe's Kylyn, recorded at Nippon Columbia in April and May 1979 with Ryuichi Sakamoto, Yasuaki Shimizu, Toshiyuki Honda and the trombonist Shigeharu Mukai. His own records of the early 1980s are Silver Shadow (1980, with Honda on alto saxophone and Ohno on trumpet), Mickey Finn (Zen, recorded August to October 1981 with a string section) and the Latin-tinged Chi Chi (Invitation, 1982). In 1984 he made the pop-leaning Twilight with the singer Mariko Hiraga and wrote "Who You Are", with Peter Barakan, for Yasuko Agawa's Los Angeles album Gravy.

Then he went back to acoustic piano. Dear Friends (JVC, 1986), all his own compositions, uses a quartet with the bassist Hideo Kawahara, the drummer Shingo Okudaira and the percussionist Tatsuji Yokoyama. Smokin' Night (JVC, 1987), recorded direct to two-track digital tape, was released in the United States on GRP, according to his record company. Autumn Leaves (JVC, 21 October 1990), with the bassist Masayuki Tawarayama and the drummer Masahiko Osaka, was also taken straight to two-track digital.

After it, multiple sclerosis, which according to his official biography had troubled him since his twenties, progressed, and he stepped back from performing. He rehabilitated through what that biography calls unyielding willpower. Seven years after Autumn Leaves he returned with Black Daffodils (JVC, 22 September 1997), recorded at Clinton Recording Studios in New York on 13 and 14 September 1996 with Ron Carter on bass and Lewis Nash on drums. It mixes standards ("In a Sentimental Mood", "There Is No Greater Love", "Blue Monk", "Oleo") with two short improvisations and the title piece. It became a Swing Journal gold disc, won an arts award from Japan's Agency for Cultural Affairs, and was released in Britain and elsewhere in Europe. In 1998 he followed it with Blue Dumplings, with Carter and the drummer Grady Tate, and the same year he played on both of Chie Ayado's first albums, For All We Know and Your Songs, co-producing and co-arranging the second.

His later years were quieter on record. He arranged and played "Nardis" and "Polka Dots and Moonbeams" for JVC's Memories of Bill Evans, recorded in the autumn of 1999. His fusion records were picked up by compilers in the 2010s and 2020s: he is on the 2018, 2021, 2023 and 2026 volumes of the J Jazz: Deep Modern Jazz From Japan series and on the DJ Notoya mix Funk Tide, a set of Tokyo jazz-funk from the Electric Bird label.

Masuda's recorded work falls into three connected bodies. The first, from Trace to the 1975 and 1976 dates with Kohsuke Mine, is hard-edged post-bop and fusion on acoustic and Fender Rhodes piano, and Discogs files Trace under Post Bop and Mickey's Mouth under Soul-Jazz, Jazz-Funk and Fusion. The second, the Electric Bird and Zen records from Moon Stone through Chi Chi, are written, arranged and often produced by Masuda himself: Latin and Brazilian rhythms, Clavinet and Minimoog funk, and in New York a pop-jazz sound shaped by Dave Matthews's string writing and session players such as Bernard Purdie, Anthony Jackson and Will Lee. The third is the acoustic trio and quartet work from Dear Friends to Black Daffodils, where the Latin tinge (Discogs lists Dear Friends under Latin Jazz and Swing) sits inside a straight piano trio.

Two features run through all three. He wrote most of his own material, and he returned to his best tunes: "Let's Get Together" has at least five recorded versions between 1976 and 1979. And his keyboard palette changed with the decade without changing his touch: Fender Rhodes, clavinet, organ and Minimoog in the 1970s, acoustic piano from the mid-1980s on. Masuda's own biographies say nothing about teachers or favourite pianists, so the clearest evidence of taste is repertoire. Black Daffodils pairs Ellington's "In a Sentimental Mood", Monk's "Blue Monk" and Rollins's "Oleo" with his own improvisations, and Blue Dumplings is mostly standards, among them "Someday My Prince Will Come" and Milt Jackson's "Bag's Groove".

He was also a pop arranger and session player. Twilight (1984), made with the singer Mariko Hiraga, is filed by Discogs under Jazz, Rock and Pop, and he wrote and arranged for vocalists such as Yasuko Agawa. That side of his work is real but small next to the catalogue as a whole, nearly all of which Discogs classifies as jazz, and the 1997 album was named a Swing Journal gold disc and won a state arts award.