Legend holds that eating mermaid flesh grants immortality. This was indeed true for the 500-year-old Yuta and his friend Mana. However, most individuals who attempt to achieve immortality either perish or mutate into monsters. Fifty-five years ago, Towa Kannagi received mermaid blood from her sister, Sawa, to cure a terminal illness. Towa now retains a youthful appearance, aside from her white hair and bestial arm. For years, she has dreamed of restoring her body, relying on blood transfusions from young corpses with the assistance of the local doctor, Shiina. Mana, whom Shiina mistakes for dead, is brought in so her blood can be used by Towa. Upon discovering that Mana is alive, how far will Towa go to restore herself? Will Yuta manage to save Mana in time?