Natsushi Aoi has had a crush since childhood. However, Natsushi kept those feelings a secret. That's because the woman he loves is almost a decade older, and she is someone he has known since childhood, a woman who now lives with him, and above all else, she is his brother Yo's girlfriend. With such complicated feelings, time passes by -- *"Why did you have to die, Yo-nii..."* The summer when the three of them played together happily will never come again. Nevertheless, summer will come again. A new summer that he will never forget.