Ep. 1: Fifteen-year-old Mana escapes a village of mermaid women with immortal Yuta after learning her fate.

1

In a Setouchi mountain village, fifteen-year-old Mana lives shackled in bed, cared for by Baba. The residents are identical old and young women who are mermaids in human form. Yuta, a five-hundred-year-old immortal human who gained his age by eating mermaid flesh, arrives seeking a mermaid. The village selects a woman to become a mermaid again through a sacrificial ocean ritual. Baba feeds this flesh to Mana to grant her immortality and rejuvenate the elders. Yuta discovers the plot and rescues Mana. During their escape, the pursuing women are flooded by sea water and revert to mermaids. Baba, an immortal human, remains with them. Yuta and Mana depart, with Yuta noting that immortality has merits despite his desire to become mortal.