The monstrous brute of a man jerked his giant cock vigorously, pointing it at his twin sons. "Get ready to get big like your daddy, boys!" the muscle monster on the couch bellowed.
Xavier stepped back. He loved being a huge muscleman, but did he want to go further? He was already utterly massive, after all! He could tell his father was ready to shoot. He turned, and rushed out of the room, heading for his closet, hoping to find something, anything, he might be able to wear. He had to get out of the house! It was clear that his father had gone insane!
Adam watched Xavier go. "Guess it's all for you now, boy," his father growled, violently double-fisting his giant rod. For a fraction of a second, Adam considered fleeing as well. But then he looked at his dad. At how immense the man had become.
Adam walked up to his father, two feet away from that giant cockhead. "Give it to me," Adam rumbled, his voice low and sensual. It drove his father over the edge.
"YES!" the giant roared, as his mutant cock became a spasm-wracked cannon, blasting cum all over Adam's muscular body. The eighteen-year-old groaned as it slammed into him with more force than he was expecting, but he kept his balance and even stepped closer to the source of all that seed. He put his hands around the big cockhead and then buried his face in it, mouth around the slit to enable him to gulp down every bit he could. He drank eagerly, slurping down the potion-enhanced jizz. He opened his mouth as wide as he could, sucking in as much of his dad's thick helmet as possible. When the huge dick finally stopped throbbing and finally gave up the last drop of seed, Adam pulled off and staggered backwards. His body felt strangely heavy, like it was stuffed full of iron or lead. He began to change.
Adam's height increased and his frame broadened out, providing space for the muscle that was swelling all over. His 250 pounds became 350, then 450, matching Xavier's dimensions. But Adam didn't stop growing there. His muscles bloated with power and size, and he howled in lust and rage as he reached 550 pounds, then 650, his muscles freakishly massive, striations running through them, veins threatening to burst free. His cock and balls similarly surged, more than doubling in size as he reached his final weight of 750 brutally massive pounds.
Adam's huge chest heaved as he took deep breaths, struggling to process what had just happened to him. He staggered away from his father and looked in a floor-to-ceiling mirror, trying to comprehend just how enormous he'd become. He had to be seven and a half feet tall, he thought to himself. His huge dick jutted out, sixteen inches of thick, brutal fucktool.
Adam barely heard the lumbering steps behind him. But the room darkened as a huge shape appeared behind him. He looked up at it, and saw his father looming over him, head brushing up against the nine-foot ceiling. "You look good, boy," the huge man rumbled, "Your brother is missing out."