Keiji Matsumoto (松本圭司) has two working lives. In Japanese pop he is a keyboardist, arranger and tour musician whose credits run from Miho Nakayama and Hitomi Shimatani to game and anime soundtracks. In fusion he is a pianist with a run of albums under his own name, a seat in T-Square's lineup at the turn of the millennium, and a quartet that plays jazz standards. Most of his Discogs entries, 128 releases in all, are the first kind. His own records are the second.

He was born in Sapporo on April 12, 1973. He started on the Electone, Yamaha's organ, at nine, at a neighbourhood music school, and went on to piano and composition. He formed a band in his last year of junior high school, moved to Tokyo after high school, and entered the Yamaha Music Academy in 1992, working as a professional keyboardist and pianist while still a student. His publisher adds that he also plays guitar, ukulele, mandolin and bass. In 1996 he joined the band of the violinist Taro Hakase.

His break into fusion came through T-Square. Hirotaka Izumi, the band's keyboardist since 1982, left in 1998, and at the end of that year Matsumoto began playing with them as a support keyboardist. After the album Sweet & Gentle (1999), on which Discogs credits him on keyboards, he became a full member. The self-titled T-Square (Sony, 2000) is the record that shows what he brought: he is credited on piano, keyboards, vibraphone, turntables and programming, and as a composer on "A Dream In A Daydream" (and its reprise), "A Nite Without Memory", "Taking Mountain (Tops)" and "Belfast Song". His publisher counts four original songs from him on that album. "Belfast Song" is also the title of the sixth track on his own debut album three years later.

The membership did not last. In 2000 the band dissolved its band format, and Matsumoto left along with the drummer Hiroyuki Noritake, the bassist Mitsuru Sutoh and the saxophonist Takahiro Miyazaki, leaving the guitarist Masahiro Andoh and the returning saxophonist Takeshi Itoh to carry T-Square forward. The friendships outlasted the lineup. Matsumoto went on to work with Noritake and Sutoh again behind saxophonist Masato Honda, and he is credited on Honda's What Is Fusion (2001) and Cross Hearts (2001), then on Crowded Colors (2003), Assemble a Crew (2004), Masato Honda With Voice Of Elements (2006), Solid State Funk (2009) and Saxes Street (2015).

His first record as a leader, Life (Green Energy, 2003), is a trio date with Sutoh on bass and Naoto on violin, viola and cello. After it he started his own label, Bootrecord, which issued the two-disc Live (2005), Promises (2005) and Life re: (2006), a band version of the Life material with two bassists, two drummers, two guitarists and strings. Live pairs two different groups: a trio of Matsumoto, Jiro Okada and Noritake on the first disc, and on the second a band with Kiichiro Komobuchi on bass, Eiji Tanaka on drums, a computer operator and the turntablist DJ Bariken. Many of its pieces turned up again on Promises. Bootrecord also released Chronochroma (2006) by the bassist Nozomu Kumagai, on which Matsumoto plays piano and keyboards.

Away from his own albums he kept a steady place in the Tokyo fusion circle. He is the keyboardist on the guitarist Kiyotsugu Amano's Book of Colors (2000) and Navajo Trail (2003), and the two formed the group Four Corners with Noritake and Komobuchi, whose self-titled album appeared on Ragmania in 2006; Japanese Wikipedia also credits him with mixing and mastering it. He is on Masayoshi Takanaka's 30th Anniversary Power Live With Friends (2001) and 2002 Live + Season's Greetings!, and again on Takanaka's Super Live 2020 (2021), and his publisher still lists Takanaka among his recent employers. For the vocalist akiko he played Wurlitzer on Upstream (2001), Rhodes on Hip Pop Bop (2002), where he also produced and arranged two tracks, and piano and arranging on Mood Indigo (2004), all for Verve. Andoh's Gameworks (2018) credits him as an arranger and on synthesizer, and he appears on two tracks of the 2022 album Unforgotten Saga by Izumi Hirotaka & Friends, the keyboardist whose seat in T-Square he later filled.

The standards are in FAZJAZ.jp, a group built around the guitarist Koichi Yabori and the drummer Masayuki Muraishi. Distortional Theory (VEGA, 2005) is made up of jazz repertoire: "A Night In Tunisia", "Invitation", "Maiden Voyage", "Naima" and "In A Sentimental Mood". Season II (2006) takes in "On Green Dolphin Street" and "Freedom Jazz Dance", and Season IV (2012) adds "So What", "Moanin'" and "Whisper Not".

The pop and game work is substantial and he does it well. He is credited on keyboards for Miho Nakayama's Olive (1998), arranged for Hitomi Shimatani and Epo, and plays piano on four tracks of the Gran Turismo 5 soundtrack (2010) and on the Super Mario Odyssey soundtrack (2018). His publisher lists, among others, Toko Furuuchi, Yoshitaka Minami, Noriyuki Makihara, Love Psychedelico, Naoto, Eikichi Yazawa and Tunnels. He has also kept releasing his own music. Apple Music lists a run of digital albums from Reminiscence (2007) through Fearless (2013), Love & Keys (2015), Stargazer (2017), Azul and Rojo (2022), Snowlore and The Winds of Spring (2024), Evanescent (2025) and, in July 2026, The Lights. He turned 53 in April 2026.

Matsumoto is best described by his instruments and his rooms rather than by a single sound. On record he is credited on acoustic piano, Rhodes, Wurlitzer, organ, vibraphone, synthesizer, turntables and programming, and on the T-Square album he is the programmer as well as the pianist. Discogs files all four of his catalogued albums under Jazz, with the styles Fusion and Smooth Jazz, and Apple Music lists his digital albums under Jazz.

His own records favour band settings that bring in more than a standard rhythm section: the string trio colours on Life and Life re:, the turntables and computer on the second disc of Live. The same musician plays "Maiden Voyage" and "Freedom Jazz Dance" with FAZJAZ.jp, so the standards repertoire is part of his working vocabulary, not a detour.

It is worth being plain about proportion. The jazz and fusion work is the smaller part of his credit list, and he would be better known to a Japanese pop audience as an arranger and tour keyboardist than as a bandleader. His own-name albums, his T-Square membership, his long association with Masato Honda, Kiyotsugu Amano and Masayoshi Takanaka, and FAZJAZ.jp are what place him in Japanese fusion; the pop credits are a parallel career, not the main thread.