A monkey too proud to admit he can't swim gets dragged to the bottom of a pool, fights a kappa for his life, and accidentally makes a friend out of it. The whole thing moves with the kind of cheerful chaos that doesn't care if you understand the logic, only that you're watching. By the time a water demon is giving swimming lessons to a drowning primate, you've already stopped asking questions and started laughing.
A swimming competition is being held among the animals, and Saru-kun the monkey refuses to admit that he cannot swim, so he enters anyway. Pride overrides sense, and he dives into the pool only to sink at once. What he finds down there is far stranger than expected: a pool floor strewn with seaweed and coral, and a kappa, a water imp from Japanese folklore, living at the bottom. The two fight, and Saru-kun manages to snatch the saucer from the kappa's head. The kappa then agrees to a bargain: he will carry Saru-kun through the water on his back if the monkey gives the saucer back. The deal lets Saru-kun glide across the pool as if he were swimming unaided, and he wins the race. How it all ends is left for the film to reveal.
