Starting this fall, Aoi will be attending a boarding school located on a distant Southern island where his father once taught at. Since all the preparations were ready, it was decided that he would move in to the school dormitory during the summer break. The island is only accessible by boat, and he was caught in a storm on the way there, but he somehow made it. Even though it was the summer break, there were still three girls who remained in the dormitory: the mischievous free spirit Sumire, the kind and cheerful Tsukino, and the cool and outwardly dependable Konoha. Moreover, his imouto Tomoe, who loves to dote on and also be doted upon by him, followed him to the island to prevent him from attending the school. The days on the island were full of fun and excitement. They showed him around the island, swam in the sea, did some preparation studying, and spent time in the library on rainy days. Every day was full of things to do. However, the summer break doesn’t seem to be ending. When Aoi became aware of this, he set out to search for the island’s secret….