Midnight Examination Room 4: Hold Me Tight (2004)

Nurse Rinko works at a hospital where intern Yoshioka joins the staff. Rinko falls in love with Yoshioka at first sight. Yoshioka becomes captivated by Ayakoji Mika, a dominatrix among the hospitalized patients. Rinko witnesses Mika engaging in sexual activity in the examination room late at night. Who is Mika's partner?