Chiyono Yoshino（吉野千代乃）may not have become a superstar in Japan but I think she has a great voice, and perhaps she represents that niche of that urban contemporary singer tackling mid-tempo material. Her brand of music probably didn't break the Top 10 on Oricon, but whenever I've heard it, it strikes me as solid and always listenable.
Case in point: her "Ai no Collage" (Love Collage) from her 3rd album "Say Goodbye" released in June 1987. With lyrics by Yoshino and music by Hideya Nakazaki（中崎英也）, it's a song that hovers between regular pop and City Pop. With a goodly amount of bass and synthesizer along with a certain type of percussion that had me thinking of exotic climes, Yoshino weaves between drama and hope within the big city. It's the type of song that still brings up images of savoring that glass of scotch in a fancy bar.