Yokosuka Girls' Marine High School is bustling as they welcome other all-girls maritime high schools for interschool competitive games. Full of excitement, students from different years gather and interact with one another as the festivals and tournaments commence. In the meantime, mixed feelings fill Akeno Misaki—captain of the distinguished Harekaze class—and her executive officer Mashiro Munetani when their instructor informs them of an opportunity for Mashiro to lead the Hiei class. As a result, Mashiro needs to make the difficult decision soon, and Akeno needs to confront the state of the situation. The pair face another challenge after Yokosuka finds itself in another pinch. A group of pirates has captured a water purification plant and sea fortress, threatening the safety of the sea. Akeno and Mashiro now must command the Harekaze class in the midst of a dire predicament—all while dealing with their own difficulties.