Until the morning with her younger sister, who was refugee home from a sudden heavy rain...

The man was thinking about marrying his girlfriend, whom he was living with. She has a younger sister Akari, who is older than her age, and she often comes to visit her house. One day, Akari, who had been refugee home from a sudden heavy rain, was soaked wet and evacuated. However, her sister is stopped at work, and the two of them are alone, a man and Akari. He usually treats her as if she were a cute little sister, but she felt a woman she normally didn't feel, losing her rationality and stole her lips. And they asked each other many times until morning came.