MIAA-224 Her sister became a stranded commuter due to the sudden downpour, and they stayed together until morning... Sachiko

The man living with his girlfriend was considering marriage. He had noticed that she had a good relationship with her sister Sachiko. One day, a sudden downpour stopped the trains and his girlfriend's sister found herself stranded, ending up at her sister's cohabiting place nearby. However, she was also stuck at work and unable to return home, leaving Sachiko, who would become his sister-in-law, alone with him. The invited Sachiko was soaked through, her underwear visible, and he felt a sensation he usually didn't, losing his reason and stealing a kiss.