Your step-father's sperm used to be top-notch, after all, we had you! But we really, really wanted two, and we've been trying for a couple years now. We went to the Dr, and well... your step-dad's sperm count and activity is frankly, horrible. I need you to impregnate me, Step-Son. I want your future sibling to be related to your step-dad, and this is the only way. I'll get naked and show you my hairy pussy, come on, don't you think I'm sexy? Let me ride your cock.