My step-sister and I have a sexual desire, stealing my wife's eyes just before giving birth...

Her husband Kenji comes to his wife Seika's parents' house to prepare for the birth. His parents' house was Iroha, the older sister who divorced Kiyoka's father several years ago. Since Kiyoka's pregnancy, Kenji has been refusing to have sex and has a sluggish desire to accumulate, and his plump body has become obsessed with the erotic pheromones of Mummu. While peering at Iroha changing clothes, Kenji can no longer hold it in, and hides Seika's eyes, approaches Iroha...