Nagisa yamada is a junior high school student residing in the rural town of tottori. her father passed away several years ago, and her mother works part-time jobs to support their family. nagisa has a practical outlook on life and wishes to graduate as soon as possible so she can live independently. on the other hand, mokuzu umino is a transfer student who appears melancholic and mysterious. she claims to be a mermaid sent from the sea on a mission to find a true friend before a storm arrives. in tottori, nagisa and mokuzu meet, form a unique bond, and work together to maintain their way of life.