One of those old...really old, as I was to discover...chestnuts that seems to pop up on Showa Era retrospectives or on kayo kyoku shows like NHK's "Kayo Concert" or "Nodo Jiman", "Futari wa Wakai" (Young Couple) is a classic that I've heard countless times.
The one time that I do remember hearing it very clearly was on the 1981 Kohaku Utagassen when a majority of the participants got together on stage for a medley of the really old kayo and, sure enough, "Futari wa Wakai" was on the singing menu. Written by Hachiro Sato （サトウ・ハチロー）and composed by Masao Koga （古賀 政男）in 1935, it's a cute and playful ditty about the love that a man and woman have for each other, presumably while strolling in the great outdoors. The first known couple of singers to have a go at it was actors Dick Mine and Reiko Hoshi （ディック・ミネ・星玲子）when it was placed as a B-side song. Just from the way of their singing at that time and the overall theme of "Futari wa Wakai", I kept thinking that Mine and Hoshi could have been the Nelson Eddy and Jeanette MacDonald of Japan.
I'm not sure if the song gets all that much exposure nowadays outside of the Showa Era retrospectives and retirement homes (can't really see this being chosen at the karaoke boxes between AKB 48 and Arashi), but a number of singing celebs have covered it over the decades. Above for instance is one take by Tora-san himself, Kiyoshi Atsumi（渥美清）, and Ikuko Masunaga（増永いく子）. Still, I think for those from certain generations, the secret to the song's success is the same secret that a lot of the upbeat kayo kyoku had....it was just perfectly made for the singalong.
And for those who aren't familiar with Eddy and MacDonald, here they are.