When 17-year-old Natsumi departs Tokyo for the sun-kissed tiny island her mother fled, it is with the intention of reconnecting with her mother’s twin sister, Reiko. The two were ama-san (traditional pearl divers) of such note that they earned the moniker of “mermaids.” However, Natsumi turning up on her aunt’s doorstep unannounced unleashes a tidal wave of resentment from Reiko as bitter memories are dredged up. Still, Natsumi is undeterred and dives into the local culture with the aim of healing family wounds while also getting herself out of some trouble.