Summer Days with Coo

One day, Koichi Uehara, a fourth-grader living in the suburbs of Tokyo, picks up a fossil that looks like a large stone while on his way home from school. To his surprise, he has picked up a baby Kappa (a Japanese mythical water creature), who has been asleep underground for the past 300 years. Koichi names this baby creature "Coo" and brings him to live with his family, and soon the two are inseparable friends. However, trouble abounds as Coo struggles to adjust to life in suburban Tokyo, and begins to miss his family, leading Koichi and Coo to embark on a summer road trip adventure in search of other Kappa.