An egg belonging to the Mythical Pokémon Manaphy is discovered floating in the sea by the mercenary pirate Phantom. However, it is swiftly stolen from him by Jackie, a Pokémon Ranger masquerading as one of Phantom’s crew. Jackie escapes aboard Phantom’s ship and slips into the Marina Group, a traveling circus family that specializes in Water‑type Pokémon, with the aim of delivering the Manaphy egg to Samiya, an undersea palace built by the People of the Water—a lineage the Marina Group themselves trace back to.
On their journey, Ash Ketchum and his faithful Pikachu, along with Brock, May, and Max, find themselves lost and crossing paths with the Marina Group. The encounter drags them into Walker’s mission, drawing them deeper into a web of loyalty, destiny, and ancient sea secrets. For the first time, the group becomes entangled in the fragile balance between adventure and responsibility as the egg’s mysterious origin begins to reveal itself. Pikachu sparks a quick, hopeful rapport with May, even as the broader pursuit intensifies and Team Rocket’s tip about the egg’s location accelerates Phantom’s relentless chase.
The tension escalates when Phantom closes in, and the egg hatches in May’s arms, binding Manaphy to her as its mother in a bond that feels inevitable and inevitable at once. This sudden connection shifts the dynamics, casting May in a protective, almost maternal light as the tiny newborn’s needs steer the course of their voyage. The group slips through ancient ruins belonging to the People of the Water, where they learn more about Samiya and the heritage that links the underwater palace to Manaphy’s own destiny. Walker, who has grown to see May and Manaphy as a hopeful future for Samiya, decides to proceed toward Samiya, even as he cautions May about the weight of what Manaphy’s role will demand.
As the journey continues, May’s close friendship with Manaphy deepens, and Lizabeth—the Marina Group’s daughter—offers May a keepsake bracelet known as the People of the Water’s Mark, a reminder of time spent together before the sea’s call becomes louder than any other promise. When May’s bandanna is swept away by the wind, Manaphy dives into the open ocean to retrieve it, prompting a dramatic chase that leads them to a submarine operated by Lizabeth. The pursuit takes them to Samiya, where the two worlds—surface life and the underwater realm—collide in a lunar eclipse that lends a surreal glow to their discoveries.
Phantom remains a constant, menacing presence, pressing forward with a single, dangerous aim. The group eventually finds Manaphy and Samiya, but Phantom has seeded grave trouble: he can unlock the Sea Crown, the palace’s central artifact composed of several large jewels. As he begins to remove the jewels, Samiya floods, threatening to drag the entire city beneath the waves. The survivors scramble for safety, using the submarine to escape while Walker confronts Phantom, managing to reconnect most of the jewels to the Crown before the flood pulls them away.
In a desperate, selfless bid to save Samiya, Manaphy returns to the Crown’s chamber with Ash, Pikachu, and May in tow. Brock and Max must depart in the submarine, while Lizabeth and the others head toward safety. The crew pieces the final jewel back into place, and the restored Crown helps Samiya rise back toward the surface. For a moment, it seems as if May’s bond with Manaphy will require a heart-wrenching goodbye, but hope still glows in the water as the city begins to emerge again.
Phantom makes a final bid by kidnapping Manaphy, but Ash, glowing with the aura from the rebuilt Sea Crown, gives chase and retrieves the young Pokémon. Phantom returns to his ship, only to be met by Manaphy’s counterattack, joined by a spirited defense from wild Water-type Pokémon, including Kyogre, which helps turn the tide. With Phantom subdued, Walker completes his mission by safely delivering Manaphy to Samiya. May and Manaphy share a heartfelt farewell as Samiya rises and then settles back into its ocean home. Phantom is arrested, and Ash and his friends part ways with the Marina Group, continuing on the road of their ongoing journey together.
