[TOMT][Anime/Animated film][1990s or earlier] Animated feature film with hippo sidekick

I remember seeing an anime film (I believe on a VHS) at my grandparents in the 1990's. I initially thought it was the Aesop's Fables film by Toei, but it wasn't after rewatching it. Maybe it was a double feature on a VHS or another Toei film? Anyway it was about a main character on an adventure with a hippo sidekick or creature resembling a hippo. I don't think it was Moonin. I also remember a climax scene with a villain, it was a very dark, cloudy, stormy setting and the villain was piloting an obscenely large ship of some sort with many dark sails or wings.