The man was thinking of marrying his cohabiting girlfriend.She had a younger sister, Akari, who was older than her, and often visited her house.One day, Akari, who was unable to return home due to a sudden heavy rain, was drenched and evacuated.However, her older sister is stuck at the company, and it's just the man and Akari.She always thought of her as her cute little sister, but when she saw her wet and translucent limbs, she felt a woman she didn't usually feel, and lost her reason and stole her lips.And they asked each other again and again until the morning came.