Those nasal pipes are undoubtedly Hiromi Go's（郷ひろみ）. "Samui Yoake" (Cold Dawn) is his 19th single from November 1976 and it's the first time I've heard it. Quite an interesting pedigree behind it; the lyricist was a man by the name of Kazuo Umezu（楳図かずお）who was not only an actor and a musician but was also an author of Japanese horror and manga, and according to his Wikipedia write-up, basically has written manga of every genre whether it be sci-fi or comedy. There is nothing particularly scary about the lyrics he wrote for "Samui Yoake"...just rather sad in that Go sings about putting on a brave face over the end of a teen romance.
The unusually cheerful melody was provided by prolific Kyohei Tsutsumi（筒美京平）. Although the song was released closer to winter, there is that summery feel to "Samui Yoake" along with those disco strings which brought things fairly close to City Pop territory. And I wondered whether this would have been something that Hiromi Iwasaki（岩崎宏美）could have tackled without raising any eyebrows considering the arrangement. As I said, it's a pretty interesting tune which got as high as No. 5 on Oricon. It is also a track on his 8th album "Machikado no Shinwa"（街かどの神話...Street Corner Myths）which was released a month after the single.