Allison 6’4 John 3’10
“Ali?” John felt his sister stir behind him. They were together in bed, naked, spooning. Allison was, of course, the very big spoon. Her two enormous breasts rested firmly against his head. As he rested against them he could hear his sister's heart beat steadily. “Wasit?” Her arm shifted down to John’s erect member, “Is it that my little brother has a big hardon for his sister?” He wiggled a little, feeling guilty. “Hmm, no!” This needed to stop before Allison went full on giant titty monster mode. “I was just, wondering about somethin’. How come I shrunk when I was with Allyssa and Brittney even though they never fed me any milk?”
For a moment, he wondered if she would answer him. “Weeeellllll,” Her hand began to move up and down the shaft of his penis. Waves of pleasure rocked him. “The truth is we had to experiment with several modifications of the virus before the current one.” fapfapfap. “It was after that little 'incident' with those two that we tried the one you currently are on. Now you only shrink when you drink from an infected woman who hasn't taken her pill.” She intensified her attentions to his cock. fapfapfapfap. Grunting a little, John spooged his load up and onto his belly. Behind him, Allison sighed contented with his release. “What…?” he said as he saw her trace a finger on his jizz covered torso. She collected a healthy dab onto her finger. She lifted it up and above him he heard a loud pop as she slide her finger, covered in his jizz, into and out of her mouth.
She moaned erotically and began to lightly thrust her pelvis against his back as she fingered herself with her free hand. She was pressing slightly down onto him, squishing him! This went on for a minute or two. Then he felt it begin. Behind him, his sister was growing! Her breasts swelled swallowing him a little more. Every part of her was expanding, swelling, lengthening. Through all of this, Allison continued to hump him lightly until she shuddered and climaxed. Now, both covered in each others sex, the pair readjusted. “Go to sleep, little guy,” she squeezed him lightly in her arms, “we have a big day tomorrow!”