Rapewoman: Dirty Sunday (1981)

Original title: レイプウーマン　淫らな日曜日

Naoko is getting a lot of obscene phone calls, so she decides to stay at her girlfriend Mari's home for awhile, afraid of a rape attack. But the telephone calls don't stop, and the mysterious pervert caller is bothering her there too. Naoko reluctantly agrees to meet meet him at a local restaurant, hoping the man will stop. When she arrives, Naoko is surprised to find the café is operated by Harada, a man whom she and Mari had liked so much in the past that, in fact, they had cat fights over him at their working places. It was due to a love triangle scuffle that they had been both fired from their previous jobs.