A commenter reminded me of this song by Seiko Matsuda（松田聖子）, "Only My Love". I didn't recognize it by title but when I heard it through the videos and the original recording, it all came back to me. The weird thing is that I hadn't realized or remembered that this was an original Seiko (the aidoru, not the watch). I had heard it before sung by other artists over the years, so I gather that it has become a standard of sorts. Still, when I saw it performed by the lady herself, I was a tad surprised.
Now "Only My Love" was written by Yoshiko Miura（三浦徳子）and composed by Yuuichiro Oda（小田裕一郎）, the same duo behind one of her big singles in Seiko-chan's early years, "Aoi Sangosho"（青い珊瑚礁）. However, unlike that soaring summery aidoru classic, "Only My Love" starts off like some sort of Walt Disney tune before it goes off into a 50s-ish bobbysoxer ballad...something more along the lines of what Mariya Takeuchi（竹内まりや）could have tackled at around the same time or even an earlier Minako Yoshida（吉田美奈子）before she discovered her inner R&B diva. There is even Seiko's attempts at a bit of falsetto just like in the way that some of those vocal groups of 60 years ago performed way back when. Speaking of her vocal style, since it was still early days, that famous Seiko delivery wasn't fully formed as of yet.
"Only My Love" was never released as an official single but it was part of Seiko's 2nd album, "North Wind" which was released in December 1980 and hit No. 1 on Oricon. The other interesting thing that I discovered about this particular song via the J-Wiki article is that whenever she performs a New Year's concert, this is the one that tends to start things off. Not a bad song to listen to while noshing down on the o-sechi.