"Pokémon Ranger and the Temple of the Sea" is a feature-length anime film set in the Pokémon universe. The narrative centers on Ash Ketchum, his Pikachu, and their companions, Brock and May, as they encounter a Pokémon Ranger named Jack Walker. Jack is tasked with protecting a mythical Water Pokémon, Manaphy, which hatches from an egg entrusted to him. Manaphy is revealed to be the "Prince of the Sea," capable of summoning the legendary Sea Temple, a hidden underwater sanctuary.

The group learns that the Sea Temple, known as the Temple of the Sea, is tied to an ancient prophecy involving Manaphy. The temple is said to hold immense power, and its location can only be revealed by Manaphy's unique ability to sense the "Sea Crown," a sacred artifact. However, the temple's power attracts the attention of a greedy pirate named Phantom, who seeks to exploit it for his own gain. Phantom and his crew relentlessly pursue Manaphy, forcing Ash, Jack, and their friends to protect the young Pokémon while unraveling the mystery of the Sea Temple.

As the journey progresses, Manaphy forms a close bond with May, who becomes its temporary caretaker. The group faces numerous challenges, including navigating treacherous waters, battling Phantom's forces, and solving the riddles of the Sea Temple. The climax occurs when the Sea Temple is finally revealed, and Manaphy must fulfill its role in the prophecy to restore balance to the ocean. The film concludes with a heartfelt farewell as Manaphy returns to its rightful place in the sea, ensuring the safety of the temple and its secrets.

The story emphasizes themes of friendship, responsibility, and the importance of protecting the natural world. Key characters include Ash, whose determination drives the group forward; May, whose nurturing relationship with Manaphy adds emotional depth; Jack, whose skills as a Pokémon Ranger are crucial to their mission; and Phantom, whose greed serves as the primary antagonist. The film blends action, adventure, and emotional moments, staying true to the core elements of the Pokémon franchise.