I'm considering Michiru Kojima（児島未散）to be one of those unsung pop singers from the 1980s and 1990s. With a nice and light voice reminiscent of aidoru singing some of that straight-ahead pop, she reminds me somewhat of Hiroko Yakushimaru（薬師丸ひろ子）and Yuki Saito（斉藤由貴）to some degree.
When I first came across this song title, I had assumed that it was "Sunset Bluebird" instead of "Sunset Boulevard"; amazing how one dash can change everything (just ask Ben Johnson...sorry, that was a very old joke there). I have seen the 1950 film noir of the same name by Billy Wilder, but I can assure you that Kojima's "Sunset Boulevard" is a whole lot more happier.
The arrangement of this song that got onto her debut album "Best Friend" back in September 1985 has that gently lilting 50s feeling which automatically had me thinking Yumi Matsutoya（松任谷由実）and Mariya Takeuchi（竹内まりや）. However, it was actually Tetsuji Hayashi（林哲司）who composed "Sunset Boulevard", and he's no slouch when it comes to mellow tunes. It's a pleasant sepia-toned 5 minutes of nostalgia with lyrics by Takashi Matsumoto（松本隆）. Quite relaxing and I can just as easily imagine the aforementioned Yakushimaru and Saito covering this one. "Sunset Boulevard" was also the B-side on Kojima's debut single, "September Monogatari"（セプテンバー物語...September Story）.
I will have to thank YouTuber オンガクch2号 since he put this one up in the last 24 hours or so. It's always nice when some of the more obscure pop songs from Japan reveal themselves.