Zoom In: Rape Apartments (1980)

Saeko, a somewhat enigmatic young woman, is brutally beaten with a rock and raped by a man wearing a dark-colored mask and black gloves. She eventually recovers, but not long afterwards a series of horrific murders begins occurring in the apartment building she lives in. When it turns out that the victims are badly beaten, then killed and their genitals burned off, Saeko begins to think she has an idea who the killer is, but realizes she may be murdered before she has a chance to expose the maniac.