Bishimai Kutsujoku no Heya

Kasumi's anxiety has been growing ever since her older sister, Mayumi, went missing over a week ago. While looking for clues, Kasumi and her friend Kensuke find a suspicious music tape in Mayumi's room. They realize that the tape contains a recording of telephone sex between Mayumi and a middle-aged man. The content of the tape turns Kensuke on, but Kasumi stubbornly refuses to go along with him, and they start fighting.

Kasumi listens to the tape after Kensuke leaves. She recognizes the man's voice. His name is Fukuzawa, Mayumi's ex-boss. He was having an affair with Mayumi. Kasumi goes to see Fukuzawa at a bar, where he shows his sadistic nature. He forces Kasumi into giving him a blowjob and then ejaculates on her face. This incident makes Kasumi realize her masochistic bloodline...

Where is Mayumi now? Kasumi makes up with Kensuke, and together, they continue searching for her missing sister. The quest reveals Mayumi's masochistic nature and allows Kasumi to experience her sister's sexual journey.