Kankoku bishimai: Futei no hitozuma (2003)

One day, Eun-joo, a married woman who has been married for two years, receives a confession of love from her younger sister's boyfriend, Tae-woo. Overwhelmed by his passion, Eun-joo crosses the line. Though wracked with guilt, she becomes addicted to sex with his strong young body. However, her younger sister becomes aware of their relationship... (South Korean softcore production imported in Japan in a dubbed version by XCES, original title unknown).