His interest developed quickly and by his late teens was singing part-time—under the stage name Kōichi Mine—in jazz bands and dance halls while a student at Rikkyo University.

The young Mine, however, abandoned the banking profession determined to make a career in music.

It was working as a singer and drummer with Noriko Awaya's backing orchestra on the dance hall circuit that Mine began to win fame.

That was followed up shortly thereafter with a cover of Dinah, which had been suggested to Mine by Teichiku's house composer, Masao Koga.

In the late 1930s, Mine was signed up by Nikkatsu Studios and played supporting roles in a number of films, including Singing Lovebirds directed by Masahiro Makino.