Ai Sayama stars as a devoted wife who finds her peaceful domestic life turned into a daily struggle. Her husband's son from a previous marriage harbors a dark, "creepy-erotic" obsession with her. With matchless stamina and a "monster-like" sex drive, the stepson forces Ai into a cycle of forbidden encounters. The film focuses on the emotional distress of a mother unable to escape the relentless lust of the "monster" living under her own roof.