I discovered Osamu Tezuka’s Mermaid at a retrospective of some of his earlier animation movies organized in 2003 by a local cinema, Rue des Feuillantines in Paris.
I absolutely loved the Mermaid, which is to me more of an animated poem. The music Prelude to the Afternoon of a Faun by Claude Debussy is equally magnificent.
I really hope they play it at the current even marvelofmanga.org, but in the meantime, I found that you can watch it on Google Videos: