The short film is about a boy who lives and works on a farm. One day when going to sell vegetables at a market, his cart breaks down. Two strangers, a frog and a mole, offer him a strange seed in exchange for the vegetables. The boy accepts and finds that the seed grows into a miniature planet. It continues growing as he tends to it, forming an atmosphere, weather systems and life. After being taken back to the city, he meets the stranger who sold the seed to him, and they release the planet into a galaxy of similar planets, where it will grow for years until becoming a real planet.
According to an ancient Japanese legend, mermaid flesh may grant immortality if eaten. However, there is a much greater chance that consumption will lead to death or transformation into a damned creature known as a Lost Soul (or Deformed Ones in the English dub). Mermaid Saga tells the tale of Yuta, an immortal who has been alive for five hundred years, who is wandering across Japan searching for a cure and meeting others whose lives have also been ruined by mermaid flesh in the process.