Fritz is an Atlantic dolphin calf living in the underwater kingdom. He serves as the devoted companion to Marina, the youngest mermaid princess. Their deep friendship anchors a central dynamic, with Fritz constantly accompanying Marina during her explorations of sunken human relics and her forbidden trips to the ocean's surface. His curiosity about the human world exists, though less intensely than Marina's. Fritz shows profound emotional investment in Marina's safety. He actively aids her first surface visit, where they observe Prince Fjord's ship caught in a storm. After Marina rescues the prince, Fritz remains her unwavering ally as she seeks transformation into a human. He supports her during the perilous journey to the Sea Witch's domain, confronting the witch directly when accusing her of causing the storm that endangered the prince. Once Marina drinks the Sea Witch's potion, gaining human legs at the cost of her voice, Fritz maintains their connection in the human world. He regularly visits the shoreline near the prince's kingdom. Marina summons him by raising her pearl hairpin, allowing Fritz to monitor her situation and offer companionship despite her inability to return to the sea. When Marina faces imminent dissolution into sea foam after the prince marries another, Fritz intervenes. He locates Marina's mermaid sisters and observes their transaction with the Sea Witch, who provides a magical knife capable of saving Marina if she kills the prince. Fritz conveys this solution to Marina. Following her ultimate choice to sacrifice herself rather than harm the prince, Fritz expresses profound grief. His cries echo her name as she transforms into sea foam and ascends toward the heavens, marking the culmination of his protective journey.