Husband Kenji visits his wife Kiyoka's parents' home to prepare for childbirth and ends up staying at the house where Kiyoka's older sister Iroha lives, now divorced from her own husband. Since Kiyoka became pregnant, she has refused sex, causing Kenji's pent-up desire to grow stronger each day. Living nearby is Iroha, whose voluptuous body and erotic aura begin to capture Kenji's attention. He starts sneaking peeks at her changing, his lust escalating beyond control. Unable to resist any longer, Kenji begins making advances toward Iroha whenever Kiyoka isn't looking.