He attracted much attention in 1979 with his exhibition "Kōen" (公園, Park) at the Komai Gallery, Tokyo. The black and white photographs were presented in a book published in 1980 that is "nominally a soft-core voyeur's manual",[9] with photographs of people at night in sexual activities in Shinjuku and Yoyogi parks (both in Tokyo), mostly with unknown spectators around them.[10] The photographs were taken with a 35 mm camera, infrared film and a flash with a special filter.[6][11][12][13]Gerry Badger and others have commented on how the photographs raise questions about the boundaries between spectator, voyeur and participant.
He died on 21 January 2022, at the age of 76.[14][15][16]
The Park. Santa Fe, NM: Radius; New York City: Yossi Milo, 2019. ISBN9781942185482. With an introduction by Yossi Milo, an essay by Aletti, and a transcript of an interview between Yoshiyuki and Araki. Includes new images and documentary materials.
Tōsatsu! Sunahama no koibito-tachi: Uwasa no rabu airando sennyū satsueiki (盗撮!砂浜の恋人たち:噂のラブアイランド潜入撮影記). Sandē-sha, 1983. ISBN978-4-88203-022-5.
"Down in the park: Yoshiyuki Kohei's nocturnes". English translation of an interview of Yoshiyuki by Nobuyoshi Araki, first published in Weekend Super in 1979. Aperture, no. 188, Fall 2007. Included within the press kit (PDF) for the Park exhibition at Yossi Milo Gallery.