Ahhh...blessed be the commenters! They have always come up with the hot tips. Chasing Showa sent me some information right now (which I will be sharing in its own article very shortly) about a Mixcloud page of the vintage kayo by someone named Megane-kun.
The first song on the playlist hit me with some Saturday night-friendly piano as part of an old-fashioned kayo/City Poppy number titled "Tasogare Matsuri" (Sunset Festival). And it is sung by none other than Momoe Yamaguchi（山口百恵）herself. There is always a certain level of joy celebrated by me whenever I initially think that I may soon becoming close to exhausting a veteran singer's worthier part of his/her discography only to discover a new unheard fun number.
"Tasogare Matsuri" is it. Written by Yoko Aki（阿木燿子）and composed by Koji Makaino（馬飼野康二）, it is one of the few times that I've observed a song written by Aki that wasn't also composed by her husband Ryudo Uzaki（宇崎竜童）. But no problems here since veteran Makaino has whipped up a rollicking beat in a Latin style that is reminiscent of Junko Yagami's（八神純子）"Mizuiro no Ame"（みずいろの雨）, an old favourite of mine and one of the first songs that I had written about on the blog. Furthermore, I am also reminded of Barry Manilow's "Copacabana" which I believe came out at around the same time.
It may have that Latin spice but instead of the bright lights of Rio, "Tasogare Matsuri" is such that I can only envision the streets of Tokyo as Momoe tackles this one with aplomb. Cherry blossom season is upon the metropolis right now so this would be a nice accompanying track to all of the drunken hilarity in Ueno Park.
One reason that I had never heard of this one before is that the song was never released as a single and except for one album, I don't have anything of a Momoe collection outside of her BEST collections. Instead it made its debut deep within one of Momoe's other BEST compilations (her 8th to be exact), which I don't have, called "The Best: Playback"（THE BEST プレイバック）which came out in June 1978. The original LP peaked at No. 8 on Oricon while the tape cassette did even better by placing at No. 3.