The opening murder in Zoom Up: Rape Site justifies the film's notoriety: it's a sadistic, mysogynistic assault that rivals anything to be found in the more extreme examples of the giallo genre, with which it bears similarities. An unseen killer wearing black leather gloves abducts a young woman, handcuffs her, and abuses her with a black dildo, before inserting a lightbulb into her privates and stomping on her abdomen, causing the glass to shatter. That's some top-level nastiness right there, although a later murder involving a bottle of acid is almost as brutal and shocking. The rest of the film, however, is far less vicious, with a bonkers plot that allows for plenty of the gusset fondling and rough sex that one expects from a standard Nikkatsu pinku.

Pretty housewife Tomoko (Erina Miyai) is having an affair with Kentarô Ômori (Takeshi Shimizu), her step-daughter's tutor. At a derelict building on an abandoned lot (the site of the murder seen in the opening sequence), the couple engage in rape role-play; afterwards, as they dress themselves, a car pulls up, so they hide. The driver and his female passenger enter the building and proceed to have sex, the woman urging her lover to choke her as they do. As the man climaxes, he overdoes the throttling and accidentally kills the woman. In a panic, he ditches her body down a hole and leaves. Tomoko is convinced that the man saw her hiding and is worried that he might find her.

While visiting a local supermarket, Tomoko thinks she recognises the killer and mistakenly attracts the man's attention. To make matters worse, she convinces Kentarô to come and take a look to verify her suspicions, during which they make their presence known to the man. Kentarô thinks that they should go to the police, but Tomoko is scared of her husband finding out about their affair.

Later, the supermarket killer pays a visit to Tomoko at her house and proceeds to rape her, an experience she positively encourages; he tells her that if she goes to the police, he will let her husband know about her infidelity and love of the rough stuff. Meanwhile, Kentarô's girlfriend Maya (Yuki Yoshizawa) suggests blackmailing Tomoko, which leads the harried housewife to take extreme measures.

As all of this is happening, the gloved maniac from the beginning of the film continues to target young women.

During the course of the film, Tomoko has lots of sex, with Kentarô, her husband, and the supermarket guy. Kentarô also has lots of sex with Maya, who happily soaps up her guy in the shower. The only people who don't have lots of sex are Tomoko's step-daughter (too young) and the black-gloved killer, who is content to just mutilate his victims' genitals.

The gloved maniac's actions aside, Zoom Up: Rape Site is fairly standard Pinku smut, with Tomoko's sexual proclivity making the rape aspect seem far less contentious than it would otherwise have been.