You look at your pretty sister, lying on the ground, having absorbed so much of your cum that it literally distorts her body. In the best possible way, though, because she looks like she's glowing, her tummy bulging, her hair damp with sweat. God, she is so pretty. She really is the perfect receptacle for your almost bottomless supply of jizz.
You have to be careful with what you say next. If every word you speak is always, immediately true, then you can't say anything flippant or sarcastic or ridiculous. Unless you want to, that is... but you should only do that when you really mean it.
With that in mind, you lie down next to your sister and start petting her breast. She shivers at your touch, like you've sent a jolt of pleasure through her body, and she wiggles in close to you, pressing her naked ass into your horse cock.
You lean in and whisper in your sister's ear: "You liked that, didn't you?"
It doesn't matter whether she liked you forcing yourself on her before, because she definitely does now. She smiles, languid and sated on the robust pounding your just gave her. "You bet I did, brother, that was the most amazing sex I think it's possible for a girl to have."
"Well let me tell you a secret, sis," you whisper softly, so that only you and she can hear it. "You and I are going to have a lot of sex from this point on, and it will always be at least that good, if not better." And sure enough, as soon as the words are out of your mouth, you know that they are absolutely true.
"Mmmm," your sister says, a sound that's almost like a purring kitten. "I don't know how it could be possible for it to be even better than what we just had, but I can't wait to find out."
"Well how does this sound, sis? You and I are fused, sexually. If one of us is aroused, both of us are aroused. And you will never want or need any cock other than mine. How does that sound to you?"
"That sounds perfect, my beautiful incestuous brother." Then she pauses, and another shiver of pleasure goes through her body. "You're aroused right now, aren't you?"
"How could I not be? I have a beautiful, willing sister who wants me, and only me, and she's naked in my arms."
Without another word, you flip your sister so she's lying on her back, and you climb aboard her. You feel her wet, willing slit against your half-erect cock, and that feeling is all the permission your body needs to get fully hard. You lift your pelvis up, and your sister bites her lip in anticipation as you line yourself up to enter her.
In seconds, you're pounding your pretty, powerless sister again. How is it possible that you have enough cum in your body this quickly to be ready to fill her up again? It doesn't matter. You have the one thing that really matters: a warm, willing vessel to receive the boundless quantities of sperm that need to go into a receptive womb.
"Oh God, bro," your sister wheezes, as breathless as if she's running a 10-K. "Oh God, yes, yes, I was made to take your cock! I LOVE YOU BRO!!! I need you! Oh God yes, yes, fill me up with your overwhelming cum! I'm your slave, bro, pound my pussy! Pound me! I love you!"
"I love you, sis," you say before you can stop yourself, and sure enough, it's true. You're absolutely in love with your sister, not as a family member, but as a woman, a beautiful and sexual woman. You never want to be away from your sister again.
And once again, you begin dropping your amazing one-hour cum load into your sister's womb. Rope after rope of potent sperm shoots out of your body and into your sister, and once again, her body expands to take it all in, not wasting one drop. You feel your sister's belly expanding under you as your potent, fertile sperm transforms her into the one thing you can love.
Finally, at long last, you're spent. You don't have even one drop of jizz left—although of course you thought she had used you up once before. Who can tell? For now, you're done, the full content of your monster balls transported safe and sound into your sister's womb. You roll off of her and look down at her beautiful, sweaty, sex-ravaged body.
"God damn, sis," you say, looking at her bulging belly. "You look like you're pregnant."