There is a legend in Japan that if one eats the flesh of a mermaid, one will become immortal. This anime recounts the story of Yuhta and Mana, an immortal boy and girl, and their experiences with a family struggling to achieve immortality at any cost.
Legend states that eating the flesh of a mermaid will bestow immortality. Yuta and Mana do not remain dead for this reason. A chance meeting with a child named Masato leads the two of them into a mystery that spans generations and will threaten their immortal lives.