Because the Naro Middle School where they were studying closed down, at the beginning of the new semester, Hikaru Sakishima (voiced by Natsuki Hanae) and her childhood sweetheart Aika Mukaido (voiced by Kana Hanazawa) and their friends Chisaki Hirata (voiced by Ai Chino) and Kaname Isagi (voiced by Ryota Oosaka) transferred to Mihama Middle School on land to continue their studies. Sakishima and his friends are the people of the sea who live on the bottom of the sea. Legend has it that a long time ago, all human beings began in the sea, and most people were fascinated by life on land and gave up the "placenta" given by God. For thousands of years, the people of the land and the people of the sea have coexisted in friction. There are conflicts, misunderstandings, and longings and yearnings between them. In the new school, Sakishima and Aika met a boy named Fumi Kihara (played by Kaito Ishikawa) who lives by the sea. From different races, the different youth stories of boys and girls are staged...