A ten-year-old boy finds a kappa fossil that wakes up as a child, and what starts as magical-pet fantasy turns into something much quieter and realer. The film doesn't hurry toward the road trip or the reunion, it sits with Kouichi learning that love sometimes means letting something go, that his suburban Tokyo routine is already a kind of loss. By the final act, you're not watching a heartwarming adventure anymore. You're watching a boy understand that some friendships are exactly as temporary as they need to be to matter forever.
Kouichi Uehara, a fourth-grader in suburban Tokyo, picks up a large stone that proves to be the fossil of a baby kappa who has slept underground for about three hundred years. He names the creature Coo, and the two become close friends as Coo quietly moves in with Kouichi's family. Life among humans is hard for Coo, though, and he misses his own kind. One hot summer day, boy and kappa set out on a road trip to look for others like him. The film mixes comedy and drama in a slice-of-life story about growing up and about being different.
