Hey, if it worked before, why not try it again? Hiromi Iwasaki（岩崎宏美）got her first No. 1 on Oricon with "Romance"（ロマンス）, thanks to the winning duo of Yu Aku and Kyohei Tsutsumi（阿久悠・筒美京平）earlier in the summer of 1975. The triumvirate did it again with her next single (her 3rd) in October of that year with "Sentimental".
I heard this on one of the two Hiromi-chan cassette tapes that Mom got me when she and Dad came back from vacation in Japan in the mid-80s. It was a BEST compilation with all her songs dating up to 1984, and all of her earliest material just happened to wrap Side B. So I got to hear "Romance" and then "Sentimental" which is a bit more whimsical-sounding than the former song. Depending on my mood, I've often it liked it better than "Romance" .
Indeed, "Sentimental" was her second No. 1. And in the short time before the end of the year, it managed to become the 78th-ranked song on the annual charts which all the way up to No. 17 for the same charts for 1976. Of course, Iwasaki would continue to do well for the next several years, but her 3rd and final No. 1 up to now wouldn't come until 1982 when she had another megahit with "Madonna Tachi no Lullaby"（聖母たちのララバイ）.
One piece of trivia I gleaned from the J-Wiki article for the song is that the original title was supposed to have been "Kanshouteki na Juu-nana Sai"（感傷的な17才...Sentimental 17）. However on the advice of a fortune teller called Shinjuku-no-Haha（新宿の母...Shinjuku Mama）, the title was changed to its katakana version of the English word since Iwasaki was told that her first three songs should have katakana titles. Thus, Singles 1-3 were "Duet", "Romance" and "Sentimental". But I guess she, the songwriters and everyone else on the staff decided to play things even more safely and dubbed the 4th single into katakana as well: "Fantasy"（ファンタジー）. I gather that it is not just athletes who are superstitious celebs.