Kimura, who works in real estate near Tokyo, is forced to abstain from sex when his wife becomes pregnant. His wife's younger sister, Risa, moves into the apartment next door to them to attend school in Tokyo. Kimura is Kokoro by Risa's open-minded personality and her young, voluptuous body, and tries desperately to suppress his sexual desires. However, he discovers a hidden camera set up by the caretaker, and is able to watch Risa at any time. He finally reaches the limits of his self-control and puts into motion a plan.