Kinjirareta Asobi (1995)

Kinjirareta Asobi 1995 / 禁じられた遊び 1995 / Forbidden Love , Forbidden Play

Eiko, a successful psychiatrist, and her husband Yohei are happy to have her sister Ayumi stay with them when she comes to Tokyo to visit her boyfriend. But no one is prepared for the feelings that develop between Yohei and Ayumi during that time. Yohei feels that Eiko's work and raising their child has separated her from him, and he can't help but fall for the beautiful, young Ayumi. Meanwhile, Ayumi catches the fancy of one of her research subjects, too. The friction between between sisters who love each other, and yet are thrown into competition with each other, fuses this enthralling story. (Source: DramaWiki)