Aika-chan no Chikyuu

The author of the manga Secrets of the World was only 12 years old, and she died days after completing it. Aika Tsubota's parents published her environmentally themed story in her memory, and this one-shot anime was the eventual result, sponsored in part by a charity opposing the pollution of the oceans. In 1995, Secrets of the World itself was animated as a two-part video series under the auspices of the Japanese Department of the Environment.

(Source: The Anime Encyclopedia)