Defining kayōkyoku is like trying to nail down konnyaku.
"Japanese standard songs" is veteran vocalist Saori Yuki's first stab at describing a musical genre that's easily recognizable but hard to construe.
"Jazz-inspired Japanese pop songs for adults," she then ventures. Warming to her subject, Yuki explains that the kayōkyoku tradition dates back to the immediate postwar era, when Japanese songwriters such as Ryoichi Hattori absorbed Western musical styles and suffused them with Japanese taste to create a new genre.