[2][3] Kosaka was a classmate and close friend of Tsutomu Hata, a former member of the House of Representatives.

He contributed to the introduction of rock and roll music in Japan and, from 1956, was one of the first to release covers of Elvis Presley in Japan, being nicknamed "Original Japanese Presley".

He drew attention to his performance in Keisuke Kinoshita's The Eternal Rainbow (1958).

[citation needed] In 1990 he published a memoir with Kawade Shobō Shinsha (which was republished by Shogakkanbunko in 2022).

[citation needed] In later years he battled with a disease while still working as an actor and singer, but eventually died of esophageal cancer in November 1997.