According to the liner notes of "Good Times Diva Vol. 6", "Kyo no Hi wa Sayonara"(Today is the Day for Goodbye) was originally written and composed by Shoichi Kaneko（金子詔一） for Moriyama as the ending theme for a student music event back in her amateur days, presumably before 1967. Even before her professional debut, the song quickly became a folk fan favourite, but its first appearance on a record was as the B-side to her 3rd single, "Koi wa Mizuiro"（恋はみずいろ....Love is the Colour of Water）, released in August 1967. Still, its fame has grown and has even become a song that has been sung by the Japanese Boy and Girl Scouts, and it has had its fair share of covers performed by acts such as Saori Minami （南沙織）and DEEN over the decades.
The lyrics has that eternal theme of friendship even under impending separation, and the melody would make for a nice lullaby. It has been used as a song for graduation ceremonies, including the ones I've attended in Gunma. There weren't a whole lot of dry eyes in the auditorium. And I'm sure at a Moriyama concert nowadays, the same would hold true.