Legend has it that devouring the flesh of a mermaid bestows immortality, a fact proven by the ageless Yuta and his companion Mana. However, others who seek eternal youth often perish or mutate into horrifying monsters. Towa Kannagi was on the brink of death when her sister Sawa administered mermaid blood to cure her ailment five and a half decades ago. Although her hair is now white and one arm is beastly, Towa retains a youthful countenance. She yearns to revive her lost body and resorts to transfusing blood from young corpses with the help of the local physician, Shiina. When Mana, mistakenly presumed dead by Doctor Shiina, is brought before Towa to be used as a blood source, Towa becomes determined to reclaim her own physical form at any cost. Will Yuta succeed in rescuing Mana before it's too late?