Manaphy, the Mythical Water-type Pokémon revered as the Prince of the Sea, emerges from an oceanic Egg tied to the ancient undersea temple Samiya. Pursued by the pirate Phantom for its sacred connection to the temple, the Egg was safeguarded by Pokémon Ranger Jack Walker before hatching under May’s care. Imprinting on May as its maternal figure, Manaphy forged an unbreakable bond with her, expressing fragmented human speech like "love you," "happy," and "May" as a testament to their emotional connection.

Its signature ability, Heart Swap, enabled consciousness transference between individuals—a power Manaphy wielded to confuse Team Rocket by swapping their minds and to relay urgent warnings to Ash during a mission to stabilize Samiya. This skill proved vital in guiding Ash to replace the temple’s destabilized Sea Crown crystals, averting its destruction.

Driven by instinct, Manaphy navigated the group to Samiya during a lunar eclipse, revealing its innate link to the temple. When Phantom’s theft of the Sea Crown’s crystals endangered the structure, Manaphy rallied Water-type Pokémon, including the legendary Kyogre, to counter the threat, displaying nascent leadership despite its infancy.

Central to Manaphy’s journey was its bond with May. Their deepening relationship led May to grapple with separation, culminating in her acceptance of Manaphy’s duty to remain as Samiya’s guardian. Their parting climaxed with Manaphy’s heartfelt "Love you, May" before it returned to the ocean.

Though biologically genderless and titled "Prince" symbolically for its sacred role, Manaphy’s narrative centers on emotional maturation—evolving from dependency on May to embracing its destiny as Samiya’s protector, underscoring themes of loyalty and growth within its mythos.