Kuroi bokan: fukei o osou (1984)

Detective Inspector Tenma Ippei and his girlfriend, female detective Date Mari, were working together to track down a brother and sister, Kyoichi, Kyoji, and Kyoko, who were serial rapists and murderers. They broke into a hospital, raped and murdered a nurse, and continued their crimes one after another, including gang-raping Tenma's partner, Misaki, before brutally murdering him along with Tenma when he arrived. Mari was dismissed from her job, but vowed revenge for Tenma and began acting on her own...