Synopsis
Sanpei is a lazy seven-year-old boy who rarely focuses on anything other than eating his school lunches. Even though his classmates constantly tease him for resembling a Kappa, he remains mostly cheerful and content living alone with his grandfather in the mountains. One day, Sanpei's school announces a swimming competition, with the grand prize being an all-expenses-paid trip to Tokyo. Determined to see his mother—who has apparently been working there for as long as he can remember—Sanpei decides to enter the contest. The problem is, Sanpei is not a very strong swimmer. So he sneaks off to a nearby lake to practice in secret. Soon, a powerful undercurrent drags him underwater, and he drowns—only to wake up in the magical realm of the Kappa. Thus begins Sanpei's journey as he befriends a Kappa child named Gartaro. Along the way, he starts to uncover the truth about his mother's whereabouts and the reason his father disappeared.