Nanako's relationship with her husband has grown distant due to their demanding work schedules, leaving her sexual desires unfulfilled. Trying to maintain their bond, she engages in phone sex with her husband, but their son Fumiya secretly witnesses the act and becomes aroused. Understanding his mother's emotional and physical loneliness, Fumiya takes matters into his own hands to comfort her. Already heightened from the phone sex, Nanako finds herself unable to resist, and an illicit, passionate relationship between mother and son begins.