In the heart of the Forest of Okoya, a Mythical Pokémon known as Zarude, voiced by Edward Bosco, stumbles upon an infant boy nestled in a cradle along the river. Unable to abandon the helpless child, Zarude chooses to adopt him, naming him Koko (portrayed by Kimlinh Tran). They venture away from Zarude's tribe, which resides within a Great Tree in the jungle that humans are strictly forbidden to enter, opting to raise Koko as a feral child in the wilderness.
Fast forward ten years, Ash Ketchum, a determined Pokémon trainer voiced by Sarah Natochenny](/actor/sarah-natochenny), along with his trusty partner Pikachu (Ikue Otani), embarks on a journey to explore the Forest of Okoya after departing from nearby Milyfa Town. In their quest to capture a wild Cramorant, Ash and Pikachu unexpectedly cross paths with a research team affiliated with the Biotope Company, a scientific organization delving into the mysteries of the jungle. Team Rocket, consisting of Jessie (voiced by Michele Knotz), James, and Meowth, discreetly trail the research team, hoping to gather intel about the Biotope Company and its leader, Dr. Zed (Billy Kametz). Among the team is Sharon (Michelle Ruff), a researcher dedicated to unlocking the secrets held by the jungle's legendary spring, rumored for its healing properties.
As Koko tends to the wildlife of the jungle, he utilizes the waters from the spring located at the giant tree to nurse injured Pokémon back to health, even though he endures the hostility of other Zarude who view him as an intruder in their territory. One day, an accident causes Koko to tumble off a waterfall, which prompts Ash to dive in and rescue him. He takes Koko to the Pokémon Center in Milyfa Town for care. Upon waking, Koko is startled and escapes, as he has never encountered any humans before. Ash and Pikachu take it upon themselves to show him the wonders of human life, forging a bond and helping him connect with his true identity.
Their adventure soon leads them to an encounter with Zarude, who reveals significant truths about Koko's origins. He guides Ash, Pikachu, and Koko to an abandoned laboratory where a photograph of Koko as an infant with his biological parents is discovered. This pivotal moment weighs heavily on Zarude, who must come to terms with his role as Koko's caregiver. Flashbacks reveal how Zarude taught Koko to call upon the jungle for assistance, illuminating their unique bond.
In a distressing turn of events, Ash finds a wallet belonging to the Biotope Company at the lab, prompting him to take Koko to their headquarters, where they meet Dr. Zed. He discloses a shocking revelation: Koko's true name is Al Molybden, the son of renowned scientists Chrom and Phossa Molybden, who tragically lost their lives in a car accident ten years prior. Koko grapples with the devastating news, fleeing to the Great Tree upon learning of his parents’ fate.
Upon arrival at the Great Tree, Koko uncovers a sinister tracking device implanted by Dr. Zed. The villain, supported by a formidable spider-like tank, confronts Koko and Ash, who attempt to thwart his plans. As Zed uses his Ariados to trap them, he launches a destructive assault on the Great Tree, which unleashes the healing spring water. In a twist of fate, Ash, Pikachu, and Koko manage to escape with unintended assistance from Team Rocket, who are grappling with the earlier Cramorant.
As chaos ensues, the Zarude tribe arrives for the rescue, compelled by Zarude's efforts to protect Koko and restore balance to the jungle. During the climactic confrontation, Koko channels the jungle's power, healing Zarude as they take down Zed's formidable machine, leading to his capture. Meanwhile, Zed's psychotic breakdown exposes his horrific crimes against Koko's parents.
In the aftermath, humans and Pokémon unite to mend the damage inflicted upon their home. Zed faces justice as Officer Jenny steps in to arrest him, aided by evidence provided by Team Rocket. Koko, ready to discover his identity and bridge the gap between humans and Pokémon, embarks on a new journey, taking with him the treasured photograph of his parents. As he and Ash depart the Forest of Okoya, they witness Zarude transforming the healing springs into a celebratory geyser, a poignant send-off for Koko as he embraces both his Zarude heritage and his human aspects. And at the Great Tree, Zarude beholds a Shiny Celebi, a symbol of the harmonious future between Pokémon.
