Since long ago, human civilization had lived on the ocean floor. However, there were many humans who wanted to live above the surface and they moved to land creating a fundamental separation between the two. After their school closes down, four 14-year-old middle school students from the sea village, Shioshishio, have to attend Mihama Middle School on the surface. What follows is their struggles to adjust to a new environment and the relationships between the sea and land people, while dealing with their own newfound feelings that have just started appearing with the end of their childhood.