Kappa no Kai-kata: How to Breed Kappas

A young man named Watashi, upon passing by a pet shop on his way home, happens upon a water Kappa in the window, which he buys, names Kaatan, and is determined to raise as a pet. Never having owned a kappa before, he relies on a book that specializes in information on how to raise and train kappa. However, Kaatan is harder to train than it immediately seems, and a lot of patience is exerted by Watashi in his effort.

Résumé

Konami's PlayStation 2 Kappa adventure game, based on the TV anime of the same name. The story takes places in Showa 40 and follows the story of a young boy named Hiroshi, who's forced to spend his summer at his grandparent's house. Hiroshi's grandparents have these green, prank-prone creatures called Kappas, and you earn your keep by raising them -- teaching them manners, guiding them and so-forth.