Summer Days with Coo

Koichi Uehara, a fourth-grader, lives in a suburb of Tokyo. One day he finds an unusual stone that turns out to be a fossilized kappa named Coo, who has slept underground for three centuries. Koichi and Coo quickly become friends, and the kappa decides to stay and live with the boy. However, modern Tokyo proves too complicated and unfamiliar a place for Coo, and he begins to long for his own kind.

To help Coo reunite with his family, Koichi and his new friend set off on an exciting journey full of adventures. Together they overcome various obstacles and discover new worlds as they search for other kappa. Their friendship and determination help them overcome every difficulty on the way to their goal, and the summer they spend together becomes a time neither of them will forget.