Koji Moriyama (森山浩二) was a Tokyo jazz singer who also played congas. He is best known for two albums with the Tsuyoshi Yamamoto Trio on the Three Blind Mice label, Night And Day (1976) and Smile (1977), and for Live At Misty (Victor, 1979), recorded at the Roppongi club where Yamamoto's trio had been the house band. Very little has been written about him. This profile rests on record credits, catalogue and retail listings, two reference databases and one interview in which Yamamoto talks about him, and it says where those sources stop.

His birth year is not settled. Discogs gives January 21, 1944, in Tokyo. A Japanese biographical dictionary hosted by Excite News, which Wikidata cites, gives January 21, 1945, and Tokyo as well. MusicBrainz and the German and Dutch Wikipedia articles give 1946 with no day or place. Only the day and the city are shared by more than one source, so the year is left open here. The same dictionary lists two other names for him, 弘山モリオ (Morio Hiroyama) and 横山守男 (Morio Yokoyama), and says he used the first of them while working in jazz coffeehouses.

The dictionary's short account of his start is the fullest early biography found. While he was a student at Shobi Gakuen, it says, he signed with the talent agency Watanabe Productions on the recommendation of the entertainer Hajime Hana (ハナ肇). He worked mainly in jazz coffeehouses as Morio Hiroyama and made his debut in February 1964 with "Washington Square" (ワシントン広場の夜はふけて). Discogs lists that record as a Columbia 7-inch single, SAS 213, released in February 1964, backed with "Marshmallow" (僕のマシュマロちゃん) and credited to 森山浩二. It is a cover-pops record rather than a jazz one: "Marshmallow" was later included on The Beginning Of Japanese Cover Pops, a five-disc Teichiku set issued in February 2016, where it sits among the Columbia tracks on disc three. The dictionary also says he worked behind the groups All Stars Wagon and Blue Jeans.

The jazz side of his story comes mostly from Tsuyoshi Yamamoto. In a May 2021 interview with the audio site Phile-web, Yamamoto described the years after he came home from a European tour with Micky Curtis's band. He worked at American military camps and clubs, and in Ginza he played as a duo with Koji Moriyama, whom he called a wonderful singer who also played conga. Together with the bassist Kinji Unno, a Latin player who had worked with the pianist Naoya Matsuoka, they formed a conga trio that worked the top Ginza clubs, and afterward went to a late-night spot in Aoyama called Kamen. In Yamamoto's account, that came before he began a nightly job as house pianist at the Roppongi club Misty in January 1974. Yamamoto does not date the conga trio more closely.

His earliest jazz credit found is on an instrumental record, as a conga player rather than a singer. On Christmas night in 1974 the Tsuyoshi Yamamoto Trio recorded Live At The Misty (Three Blind Mice TBM-37) at the club, with Akira Daiyoshi on bass and Toshio Osumi on drums. Discogs credits Koji Moriyama with congas, and a 1999 XRCD edition narrows the credit to the first four tracks, which are the four on the original LP: "Sweet Georgia Brown," "The Loving Touch," "Dark Eyes" and "Moanin'." A Billboard Japan listing for the 2013 reissue notes that Yamamoto's trio had been Misty's house trio for a year by then.

In 1975 the trio, with Moriyama on vocals, played a private concert in the Hida-Takayama area. On August 23, 1975, in the Yoshijima house in Takayama, Gifu, they performed for local jazz fans, and Yoshihiko Kannari recorded it on quarter-inch analog tape. The six tracks stayed unissued until Master Music released them as the XRCD24 Hida-Takayama Jazz Session in 2018, billed to the Tsuyoshi Yamamoto Trio with Koji Moriyama. Akira Daiyoshi is the bassist there, and the repertoire runs from "My Funny Valentine" and "'S Wonderful" to "You Are My Sunshine" and a nineteen-minute "Down Town." It is a 2018 release of a 1975 recording, not a 2018 performance.

Night And Day came four months after that concert. The Three Blind Mice LP, TBM-58, was recorded on December 16, 1975, at Aoi Studio in Tokyo and released in 1976. Moriyama sings and plays congas, Yamamoto is on piano, Nobuyoshi Ino on bass and Tetsujiro Obara on drums. The label's owner Takeshi Fujii is credited as producer and Yoshihiko Kannari as recording engineer, and the seven tracks are all standards: "Night And Day," "The More I See You," "There'll Never Be Another You," "My Foolish Heart," "For Once In My Life," "My Funny Valentine" and "Bye Bye Blackbird." The collector Takami Aoki, on his jazz-collection site, calls it Moriyama's first album and notes that the CD edition carries English lyrics and Japanese liner notes by Kei Aoki. Disk Union's shop listing describes it as a stylish vocal and scat record with a swing feel unusual for a Japanese singer.

Smile (Three Blind Mice TBM-5002) was recorded on August 29 and 30, 1977, at Toshiba EMI Studio No. 1 and released on December 5, 1977. Yamamoto, Ino and Toshio Osumi are the trio, and the nine tracks include "Lover Come Back To Me," "Smile," "When Johanna Loved Me," "Around The World," "The Very Thought Of You" and "All Of Me." A retail listing for the 2001 CD, the third title in the label's TBM 1800 series, calls it a ballad album. The paper band on the 2013 reissue, signed Koki Hanawa (塙耕記), calls Moriyama an urban-style vocalist and singles out the fast scat on "Around The World" and the bossa-style arrangement of "Day By Day." Two of his tracks, "Night And Day" from the first album and "Around The World" from Smile, were included on Nippon Jazz, a 2018 Three Blind Mice compilation.

His third album under his own name was Live At Misty, recorded at the Roppongi club on June 6 and 7, 1979, and issued on Victor (SJX-20149). It is not a Yamamoto record. The band is Kenji Kosei (弘勢憲二) on piano and electric piano, Masayuki Takayanagi on guitar, Yasuhito Mori on bass and Takeshi Watanabe on drums, with Moriyama on vocals, according to Discogs. The twelve tracks are again standards, from "I'm In The Mood For Love," "Days Of Wine And Roses" and "The Girl From Ipanema" to "My Funny Valentine," and the German and Dutch Wikipedia articles both list the same lineup, citing Tom Lord's discography. Think! Records reissued it on CD in November 2007 (THCD-070). Aoki, who owns the LP, remembers Misty as a basement room with a domed plaster ceiling and the piano at its centre, and says it closed in 1981.

After 1979 the trail goes quiet. No later album of his own turned up, and his records have stayed available through reissues of the Three Blind Mice titles: Blu-spec CDs from Think! Records in 2013 and a second set from Craftman Records in 2019, which also covered Yamamoto's Live At The Misty; the Billboard Japan listing for that 2019 CD names Moriyama among the players. Aoki's collection site describes him as a jazz singer, conga player and tap dancer, but that line appears on no other page found. The Excite dictionary page was last updated in 2021. No obituary or notice of death was found, and no recent interview, so his later life is undocumented here and no claim is made about it.

His repertoire was the American songbook sung in English: Cole Porter's "Night And Day" gave the first album its title, and the rest of his three albums stay with "My Funny Valentine," "For Once In My Life," "All Of Me," "The Girl From Ipanema" and similar material. On the Three Blind Mice records he sings with a piano trio, and the conga playing is credited to him on Night And Day. Two retail sources describe his sound: Disk Union's listing for Night And Day stresses a swing feel unusual for a Japanese singer, along with stylish vocals and scat, and the 2013 Smile paper band stresses fast scat and a bossa treatment. Discogs files the two Three Blind Mice albums under the style Vocal, and Live At Misty under Post Bop and Latin Jazz.

Aoki writes that Moriyama and Yamamoto belong to the second generation of postwar Japanese jazz, after figures such as Sadao Watanabe and Toshiko Akiyoshi, and says he had devoted fans in his day. No source found names his influences or teachers, so none are listed here.

On scope, his recorded output is small, and everything after the 1964 cover-pops single is jazz; the Excite entry places his early club work in jazz coffeehouses. All three of his own albums are tagged Jazz on Discogs, and MusicBrainz tags him jazz and pop.