One morning, Wataru Hoshino found a sleeping girl - in nothing but her underwear - in his room. When she woke up, she quickly escaped by jumping out of the window, but not without punching Wataru in the face first. This girl, Rinna Sawaki, ends up being a transfer student of Wataru's school, as well as the new roommate of Wataru's dormitory. He lives with four other girls and their school teacher, but due to Temizugawa Heavy Industry's cancellation of their aviation branch - South Sakojima Island's major company - the families involved with the corporation have to be evacuated in one year. As a result of this, the four girls have to leave the island in one year's time. Knowing this, Rinna refuses to become friends with Wataru and the other girls, because of the pain that she might experience as a result of their eventual separation. However, Wataru disagrees with her, and over the course of the year, tries to convince her otherwise. 在稍稍离开大陆的南方小岛上,只要登上层层石梯就能把所有景色尽收眼底,主人公星野航(ほしの·わたる)就读的学校就坐落在这个小岛上。但是随着原先岛上的大部分企业渐渐撤离,学校的人数也开始渐渐减少。在岛上的另一个高台上,是用学校的旧校舍改装的宿舍,星野航和所有的女主角们就住在那所宿舍之中,但是有一天来了一名神秘的转校生,在他入住宿舍后岛上的时空开始反转错乱,忙乱而又快乐的学习生活就此开始……