Kayo Kishimoto (25 years old) works at a company that sells used office equipment. Despite having a boyfriend of marriageable age, she secretly continues to think about her silent, moderately muscular stepfather who lives with her. Although she has no desire to break up the family, she masturbates whenever she has free time, imagining her stepfather's powerful penis. The more she rubs her crotch with her fingers, the stronger her desire for her stepfather becomes. One day, she receives the good news that her mother will be three hours late coming home...