Nobody talks about this one. It's a 1971 pilot that sat in a vault for thirty years, a Western-style take on Triton that exists in this weird space between Japanese and international animation aesthetics, frozen in amber before the series it was meant to sell ever became what it actually was. You're watching a ghost of an idea, a path not taken. The craftsmanship is there, clean lines, deliberate character work, but what makes it hit is knowing this was someone's pitch to the world, made decades before anyone outside Japan would care about anime at all.
Aoi Triton is the pilot film for the Umi no Triton anime, a single fantasy special produced in October 1971. It was made as a pitch to sell the series to overseas buyers, and it draws Triton in a more Western-looking style than the eventual show. The pilot stayed out of public view for close to thirty years, until it appeared as part of the DVD release of the film version.