Mermaid Yuna Croft, Queen of the Seas, saves human Prince Henry Fox from a shipwreck on her coronation day, and the two fall in love. Defying her grandmother’s warning, Yuna abandons her throne, drinks a potion to gain human legs amid agonizing pain and follows Henry to his royal court, with a magic crystal bottle left for her to return to the ocean. Seeking political and maritime advantages, Henry betrays his vow, chooses to marry Princess Lilian from a neighboring kingdom and imprisons and humiliates Yuna. Yuna exhausts her power for others yet her merit is stolen and she endures endless torments. Her loyal dolphin‑spirit sacrifices itself to protect her. Poisoned by Lilian, Yuna fakes her death, retrieves the crystal bottle and reclaims her sea throne, unleashing giant waves to destroy Henry’s fleets. Henry finally sees the truth and calls off the engagement, while wrongdoers get their due punishment. Henry repents bitterly by the seashore, but Yuna watches coldly from the deep sea; his suffering is not even a fraction of what she endured.
