With his wife close to giving birth, her mother Tina comes to Tokyo to help care for her. Tina eases his wife’s burden, but he has a problem of his own: his wife banned him from masturbating a month ago, and he is struggling to control his pent-up lust. Though he knows it is wrong, he cannot stop staring at Tina’s voluptuous body. He even spies on her naked in the bath until she catches him: “Ren, you’re watching me, aren’t you?” Once his secret is exposed, the son-in-law and mother-in-law cross the line into repeated breeding sex.