Inferno Jūrin (1997)

Reiko comes to Tokyo to search for her sister Sumiko, who has disappeared. However, before she knows it, she has fallen in love with her sister's boyfriend, Kazuyuki. A hidden camera captures the two of them engaged in lewd behavior. Behind it shine the mysterious eyes of the man and woman who kidnapped Sumiko. Now another woman is about to become the beasts' prey...