"Dolphin Prince" centers on a young man named Kai, who lives in a coastal town where the ocean plays a central role in daily life. One day, while exploring a mysterious underwater cave, Kai encounters a magical dolphin named Nalu, who reveals himself to be the prince of an ancient underwater kingdom. Nalu explains that his kingdom is under threat from a dark force that seeks to corrupt the oceans and destroy the balance between land and sea. To combat this, Nalu bestows Kai with the ability to transform into a human-dolphin hybrid, granting him enhanced strength, agility, and the power to communicate with marine life.

As Kai embraces his new role as the Dolphin Prince, he is joined by a group of allies, including Marina, a marine biologist with a deep understanding of ocean ecosystems, and Taro, a tech-savvy inventor who creates gadgets to aid their missions. Together, they embark on a series of adventures to protect the oceans, facing off against the dark force and its minions, which manifest as monstrous sea creatures and corrupted humans. Each episode explores a different environmental issue, such as pollution, overfishing, and habitat destruction, tying the narrative to real-world concerns.

The series balances episodic storytelling with an overarching plotline, as Kai and his team uncover the origins of the dark force and its connection to an ancient prophecy. Along the way, they encounter various underwater civilizations, each with unique cultures and challenges, further expanding the world-building. The characters grow through their experiences, with Kai learning to balance his human life with his responsibilities as the Dolphin Prince, Marina deepening her connection to the ocean, and Taro refining his inventions to better support the team.

The antagonist, a shadowy figure known as Abyssos, seeks to harness the power of the ocean for his own destructive purposes. Abyssos is revealed to have a tragic backstory tied to the underwater kingdom, adding complexity to his motivations. As the series progresses, Kai and his allies uncover the truth about Abyssos and the prophecy, leading to a climactic battle that determines the fate of both the ocean and the surface world. The narrative concludes with a resolution that emphasizes the importance of harmony between humans and nature, leaving room for potential future adventures.