Toshiyuki Sekine (関根敏行) was born in Tokyo on 10 January 1955 and came to jazz by way of a pop record. In high school he bought a Sergio Mendes and Brasil '66 album, which pulled him toward bossa nova and then outward to rock, Wes Montgomery and John Coltrane. By sixteen he was teaching himself jazz piano from records by Bud Powell, Wynton Kelly, Bill Evans, Phineas Newborn Jr., Herbie Hancock and João Gilberto, and he turned professional in 1974. In 1975 he became the first pianist at Sometime, the Kichijoji jazz club. His own account names the players he worked with in those early years: the bassist Takashi Mizuhashi, the alto saxophonist Yoshio Otomo, the bassist Osamu Kawakami, the tenor saxophonist Takao Uematsu, the drummer Toshio Osumi and the tenor saxophonist Mabumi Yamaguchi, alongside the drummer O. "Jess" Kurata and Masayuki Ise.

His first record came out in an edition of 100 copies. Stop Over was cut on 15 August 1976 for Smile, a small label whose first release it was, and it is billed to the Hideto Sasaki and Toshiyuki Sekine Quartet + 1: Sasaki on trumpet, Noriyasu Watanabe on alto saxophone, Sekine on piano, Kei Narita on bass and Takashi Kurosaki on drums. It is an all-acoustic hard bop session built on Sasaki's title track and pieces by Denny Zeitlin, Cedar Walton, Tadd Dameron and Bobby Hutcherson, and for decades it circulated mostly as a collector's want-list item. BBE reissued it in its J Jazz Masterclass series, with Sekine's approval and new sleeve notes, and put its title track on the 2019 compilation J Jazz: Deep Modern Jazz From Japan 1969-1983 (Volume 2).

Two trio albums followed in 1978. Love For Sale (Audio Lab. Record, released 12 May 1978) is a piano trio with Osamu Kawakami on bass and Hideo Yamaki on drums, and his English-language biography presents it as his first album under his own name. Strode Road (Smile, 1978) is a second trio date with Narita and Kurosaki, pressed privately in 200 copies. Around them he was in demand as a sideman. He played on Kawakami's own first record, Jump For Joy (Audio Lab. Record, 1977), one of two pianists beside Masanori Sasaji with Yasuaki Shimizu on tenor saxophone, and in 1978 he played electric piano in Otomo's quartet on As A Child (Seven Seas), an electric-leaning session with Satoshi Kosugi and Akiyoshi Yoshino. He also appears on keyboards and harpsichord on Nanako Satoh's pop album Pillow Talk (Blow Up, 1978).

From 1979 to 1984 he was a member of the drummer George Otsuka's group, and he is credited on synthesizer on Maracaibo (Trio Records, 1980). The band on that record also has Miroslav Vitous on electric bass and synthesizer, Naná Vasconcelos on percussion and voice, Mabumi Yamaguchi on tenor saxophone and Tsunehide Matsuki on electric guitar. He then led his own groups in Tokyo until he stepped away from music. In 1985 he heard the improvising of Idaki Shin (いだきしん), and in 1988 he left performing to promote Idaki's concerts in Japan and abroad. After a private concert with Idaki in 1998 he wanted to play again, and he returned to live work in 2002 after a break of thirteen years.

He rebuilt his career around his own label. In 2004 he formed the Nippon Soul Jazz Band, whose first record, Ignition (誕生), was released on 25 February 2007 on Mugigi Records, the label he runs from Takanawa in Minato Ward; the same year he produced the vocalist Ayumi Kawano's debut album Fragrance on the label. Dancing (舞), a trio album recorded in October 2010 with the bassist Norikatsu Koreyasu and the drummer Takayuki Koizumi, followed on 14 May 2011. In those years he also played on the singer Takako Afuso's My Blues (M&I, 2012), for which he wrote arrangements, on Masayuki Kume's March 11th (Kidman, 2013), on How Insensitive (2014) by The Three with Mizuhashi and the drummer Kazuya Ishida, and on two of Toshio Osumi's albums for M&I, Carry On (2014) and Caravan (2019). His own biography adds performances with the tenor saxophonists Steve Grossman in 2014 and Eric Alexander in 2016.

I Love Music (Owl Wing Record, 2021), recorded on 31 August 2021 at Owl Wing Studio in Tokyo, is his first solo piano album. Dedication (Mugigi Records, 2023) was recorded on 6 December 2022 at NK Sound Tokyo with the bassist Hiroshi Yoshino and Koizumi, a set of standards from "Stella By Starlight" to "Days Of Wine And Roses" that closes with "Waseda-dori no Theme" (早稲田通りのテーマ), a title that also opens Ignition; his site counts it as his seventh album as a leader. By then the 1970s records had found a second audience: Love For Sale was reissued on vinyl by Audio Lab in 2025, Strode Road was reissued by Craftman Records, and Disk Union describes both as strongly received in Asia. In April 2025 his trio played Jazz at Lincoln Center Shanghai and, the next night, the Wukesong Musicfans Arts Space in Beijing.

Longing (Somethin' Cool, SCOL1085), released on CD on 5 August 2026 and on vinyl on 2 September, is the Yoshino and Koizumi trio recorded on 18 November 2025 at NK Sound Tokyo. It contains "Little B's Poem," the Hutcherson tune he had already recorded on Stop Over in 1976, so the new record comes almost fifty years after the first. He turned 71 in January 2026 and plays regularly in Tokyo clubs, including Shinjuku Pit Inn, and teaches jazz piano.

Sekine is a hard bop and straight-ahead pianist whose reference points are the ones he names himself: Bud Powell, Wynton Kelly, Bill Evans and Phineas Newborn Jr., Herbie Hancock as the modern example, and the bossa nova of Sergio Mendes and João Gilberto behind them. Jazzwise described Stop Over as an acoustic hard bop date in the manner of a late-1950s Blue Note session, and one review of the album likens his touch to Horace Silver's. A shop description of Longing calls it funky, bop-inflected hard bop with occasional modal passages, and Disk Union stresses groove and melody.

The piano trio is his main format. Love For Sale and Strode Road in 1978, Dancing in 2011, Dedication in 2023 and Longing in 2026 all pair standards, tunes by Walton, Hutcherson or Dameron, and a few originals, and a retailer's description of Love For Sale likens it to the Three Blind Mice piano trio records of the 1970s. Away from the trio he has stretched in three directions: electric piano and synthesizer in the late-1970s sessions with Otomo and Otsuka, a soul jazz band format on Ignition, and the unaccompanied I Love Music.