After returning home with his girlfriend, the young man met Akari, a plump and attractive high school girl, and began to develop feelings for her due to her cuteness and allure, which were no less than those of his girlfriend. On a rainy evening, the younger sister, who had forgotten her raincoat while attending extra classes, had to seek temporary shelter at her sister's house. However, only her boyfriend was at home as her sister was unable to return due to the heavy rain. Fearing the thunder, as soon as she stepped into the house, she quickly knelt down and hugged his legs tightly due to the loud thunder, revealing her seductive curves in her wet schoolgirl uniform. Unable to control himself, he then pushed her onto the sofa and began to satisfy his desires, despite her initial timid protests. This was not the end of it, as from then on, she frequently felt a strong sexual desire and took the opportunity to continue her illicit affair with him - the soon-to-be husband of her sister - while her sister was away on a business trip for three days.