The man who lived with her was thinking of getting married.She also noticed that she had a good relationship with her younger sister, Sachiko.One day, the train stopped due to a sudden heavy rain, and her sister was stranded at home, so she came to her sister's cohabitation near her.However, she is stuck at her place of work and is stranded at home, leaving her alone with Sachiko, who becomes her sister-in-law.Sachiko, who she invited in, is soaked all over her body and her underwear is transparent, and she feels a woman she doesn't usually feel, loses her reason, and steals her lips.