As I've said a number of times before, if I had to opt for a favourite sub-genre within Japanese popular music over the past few decades, it would be City Pop. Jazz is also music that I came to like while I was living in Japan during those 17 years, and like J-Pop/kayo kyoku, it's also pretty broad with a number of different sub-genres. Choosing for a particular sub-genre I like in jazz, I guess I would have to go with what I believe was called Cool Jazz in the 1950s, so pianist Bill Evans, Chet Baker and basically anyone with a trio, quartet or quintet who performed those laidback pieces in a smoky nightclub way back when.
Not too long ago, I encountered this YouTube video with a singer by the name of Yoshiko Sai（佐井好子）. The Nara-born singer and composer initially had a singing career between 1975 and 1979 beginning with her debut album, "Mangenkyo"（萬花鏡...Kaleidoscope）and her first single, "Hatachi ni Nareba"（二十才になれば...When I Become 20）. She then took a very long break before starting things up again in 2001.
Her final album before stopping in 1979 was "Chou no Sumu Heya"（蝶のすむ部屋...A Butterfly's Room）from 1978 and the song above is from that release, "Kaasama e" (To Mother). To me, Sai's voice and the instruments gave off that feeling of listening to the song in that smoky nightclub with Sai herself being that lady with the ready torch song.
Also listening to excerpts from "Mangekyo", I don't think Sai is by definition a jazz singer (perhaps more along the lines of folk/New Music) but with "Kaasama e", she illustrated that she did have some chops for intimate jazz.