The film tells the story of Aiko, a 35-year-old mute woman who works in a bowling alley, and her brief romance with Yoshioka, a younger man who works as a postal carrier. The two meet when Aiko accidentally knocks Yoshioka off his bicycle, and they have a sexual encounter soon after. Aiko begins preparing lunchboxes and giving them to Yoshioka at his workplace as a way of expressing affection, which she cannot do verbally.

The Slit-Mouthed Woman is a striking example of Pink Cinema that mixes horror with eroticism in a way that is both unsettling and genuinely original. A young couple enter a hospital after rumours that a demonic spirit known as the slit mouthed woman had been seen there. Once inside, they are possessed by an overwhelming desire to have sex and sneak off into an empty room to satiate their lusts. Then out of the darkness a perverse and disfigured woman appears and confronts them.The Slit-Mouthed Woman, a.k.a Kuchisake, is an original hybrid of pink erotica and horror from the controversial J-sploitation director Takuaki Hashiguchi whose previous films include the disturbingly nasty Woman Prisoner Torture. The Slit-Mouthed Woman features impressive special make-up effects from Takashi Oda, who worked alongside the acclaimed actor/director Beat Takeshi Kitano on his Yakuza action film Sonatine.