Living alone due to her husband's work transfer, mother Maiko moves in with her daughter and son-in-law Hikaru, pretending to enjoy a harmonious family life. Behind closed doors, however, Maiko suffers from mounting sexual frustration, spending her nights indulging in frequent masturbation. Unbeknownst to her, Hikaru secretly spies on her intimate moments. Once he discovers Maiko's obsession with big cocks, her desire intensifies, and she begins shamelessly seducing him with increasingly lewd advances. Unable to resist his stepmother's relentless lustful behavior any longer, Hikaru finally gives in and loses control.