Well, there was another Tulip tune used in the show in one of the last episodes, and it was such that it probably had viewers weeping an ocean's worth of tears. That would be "Seishun no Kage" (Shadows of Youth), which was actually the band's 6th single from June 1974. Lyricist and composer and singer Kazuo Zaitsu（財津和夫）delivered this song in such a mournful way that if anyone remembers the relevant scenes from "Hitotsu Yane no Shita", it would probably cause a Pavlovian reaction in their lachrymal glands.
Apparently, according to a Chunichi Shimbun article in 2014 via J-Wiki, Zaitsu had created "Seishun no Kage" with The Beatles' "Long and Winding Road" in mind. The song actually talks of a time after a man and a woman had split up from a relationship but supposedly, the number has often been used at wedding receptions. Go figure on that. In any case, "Seishun no Kage" got as high as No. 46 on Oricon. It's also a track on Tulip's 3rd album "Take Off" from April 1974.
Masaharu Fukuyama（福山雅治）, who starred as one of the brothers in the original "Hitotsu Yane no Shita" and its sequel, provided a cover of "Seishun no Kage" in his 2002 album "Fukuyama Engineering Soundtrack ~ The Golden Oldies"（「福山エンヂニヤリング」サウンドトラック The Golden Oldies）. Released in June of that year, it peaked at No. 2 and ended up as the 25th-ranked album of the year.