Deep within the Okoya forest, the legendary Pokémon Zarude reside in a clan and enforce a rigid rule that bars outsiders from entering their domain. Elsewhere in the wilderness lives Koko, a human boy nurtured by a solitary Zarude who departed from the clan. Koko has grown up never questioning that he is a Zarude. Yet one day, an accidental encounter with Satoshi and Pikachu gives Koko his first human companion. Is he truly a Pokémon? Or is he, in fact, a human? When peril looms over the jungle, the ties between Pokémon and humans—and the affection shared by parent and child—will be tested in depth.