Under a piercing blue sky, surrounded by crystal clear water, the sun scorched Ao Hoshizaki's skin. Gazing at the summer scenery, it seemed as if the girl was left behind in a world that she had wandered into. At a school adrift in the distance, there lived three girls who had lost their memories. The only thing they could remember was their names. Ao, shrouded in confusion, begins to lead a communal life with the girls as they seek clues about a way to return to their original world. One day, in this world where the school was surrounded by nothing but water, a path suddenly appeared. At the end of the path was a mysterious location, where familiar things existed. In order to understand, the girls decided to venture forward, but as soon as they took their first steps, they encountered a monster they had never seen before. But when they thought things had become hopeless, the girls obtain a mysterious power. If the girls solve the mystery, what will they obtain?