A young mermaid emerges from the sea and finds herself entangled with a wealthy, spoiled young man. Initially repulsed by his arrogant behavior, she nevertheless begins to change him, and he gradually transforms into a devoted husband. Their romance is complicated by her fish-like scales and the secrets of her true nature. This story is one of three contained in the volume. The title story, Eien no Jewel, serves as the third continuation of the series Mayonaka no Jewel, continuing the romantic and ecchi adventures of its established characters. The volume also includes the one-shot Kake x Ochi, which follows a separate pair of lovers whose relationship is tested by a wager and a fall from grace. Across all narratives, the manga explores themes of personal transformation, the clash between human and supernatural worlds, and the trials of first love, all within a shoujo romance style with suggestive moments.