Having purchased Nippon Girls and Nippon Girls 2 on vinyl and finding both albums filled with liner notes, I was prepared for some cultural spelunking.
First up: the movie "Susume! Jagazu tekizen joriku" (1968) [ IMDB ]. Sheila Burgel, author of the wonderful liner notes for NG2, commented in a paragraph on Akiko Nakamura that There is a fantastic scene in GS [Group Sound] film Susume! Jaguars Tekizen Jourika (Landing In The Presence Of The enemy The Jaguars Advance!) with Akiko Nakamura performing 'Niji-iro No Mizu Umi' in knee-high socks, a black pinafore and what appears to be an enourmous tutu as a top.
I eventually found the IMDB reference with Akiko's name but the only hit with that wonderful translated title is for an Australian band who, though I'm sure are fine musicians, were just not what I was looking for. I eventually got to the IMDB link after finding a blog entry on "DIE, DANGER, DIE, DIE, KILL!" titled "Hey You, Go! (Japan, 1968)" about a movie with Akiko in it. Definitely worth a read and his video review with clips from the movie is here:
I have no idea how one title got translated to another, and Todd at DDDDK! reviewed a copy he got with no subtitles, so no insight there. He described it as similar to a Beatles or Monkeys film from the same era. I had watched the Monkeys' film Head and was... disappointed. Maybe better in a foreign language? According to DDDDK!, the movie is a showcase for the GS band The Jaguars--really just the lead singer--and Akiko plays his love interest. The song of hers we get on NG2 is "Namida no Mori no Monogatari" ("The Forest of Tears", worth listening to while it's up on DailyMotion). The one from the movie (YouTube below, while it lasts) sounds like it utilizes the chipmonk speedup that Burgel says was popular at the time (you wouldn't believe how many Japanese records from the 60s regularly employed this hilarious technique
). Not as recommended.