This beautiful Toei Animation film, Hans Christian Andersen's The Little Mermaid, was part of a Japanese film festival in 1975, and later reached the U.S. in 1979. My dad taped it off the TV for me when I was small—we were going on vacation and my parents worried I'd get upset if there were no familiar kids' programs.
This tragedy was upsetting anyway: It portrays the classic Danish fairy tale closer to the grim original—unlike in Disney's happily-ever-after, this story sees the mermaid princess thwarted by love, surrendering her own life. I used to heave full-body sobs each time I watched her spirit rise through the air, in the form of rainbow seafoam bubbles (my concerned mother kept trying to make me stop watching it so much, but I couldn't be stopped).
It's clear here how heavily Disney was inspired by the Toei film, from the heroine's fish companion to her favoring a statue of the prince. Other elements will also be familiar. Neither movie, though, contains the sad detail from the original tale whereby the mermaid consents to experiencing constant excruciating, knife-like pain from her new human legs and feet.