Kappa no Kaikata(2004)

A young man passes a pet shop on his way home, and seeing a kappa in the window, decides to buy it on a whim. He brings the creature home, and names him Kaatan. He's never owned a kappa before, so he relies heavily on a book he purchased on the subject of raising and training kappa. The books gives several good tips for bringing up a smart and well behaved kappa, and it all seems very simple. Unfortunately, putting these techniques into practice and actually making them work is not quite as easy as the book implies. Kaatan seems to understand things at first, but usually ends up either forgetting what he's learned, or isn't interested in learning in the first place. However, this particular young man has a lot of patience, and continues his possibly fruitless effort to raise Kaatan into a pet he can be proud of.

(Source: Anime News Network)