Yusaku is overwhelmed by the pressure of his thesis while being tormented by his alluring and uninhibited stepsister, Maki. He realizes she is always watching him, and knowing this, he indulges in bold masturbation. At the dining table, she openly exposes her crotch, her behavior shamelessly overt even as she sips wine. Every time her husband goes on a business trip, Maki tells Yusaku, "It's your duty now," and launches into intense aggressive sex. One night, when her husband passes out drunk, Maki pounces on Yusaku like an aroused female cat, whispering, "Keep going until morning." This scene reveals the unique, twisted relationship unfolding between the two.