With his wife Honoka's delivery date rapidly approaching, husband Kenji finds himself filled with both excitement and anxiety. One day, his stepsister Mako comes over to help with household chores, gradually becoming a presence that stirs emotions within him. Mako is adorable, has a great figure, and possesses a warm, caring personality. As Kenji's marital life with Honoka remains on hold, his testicles become painfully full and tense. Unable to endure it any longer, he finally takes action.