The Murakami family is a single-parent household. Their only son, Satoru, has become a university student and recently got a girlfriend. While his mother, Ryoko, feels relieved to see her son growing up, she also feels lonely. One night, Ryoko makes dinner and waits for Satoru to come home, but he doesn't get home until late at night... During that time, Ryoko suspects that Satoru is flirting with his girlfriend. Not wanting her only son, whom she has raised with great care, to be taken away, Ryoko tries to get Satoru's attention...