My Brother's Wife: In a Dream (1988)

The story centers on the steadfast eldest son, the caring and alluring nurse eldest daughter, the ambitious, fast-rising second son, and the vivacious, free-spirited youngest daughter. United by the heavy burden of an enormous debt inherited from their late parents a decade ago, their fragile stability is upended when the irresistibly beautiful and enigmatic Rinko appears on the scene as a marriage prospect for the eldest son. Her seductive allure triggers a chain reaction that sends shockwaves through the family, igniting passions and secrets in a swirl of scandalous incestuous desire.