Nate started putting on his dad's boxers to get dressed and head back upstairs, his dad doing the same in his body. Nate felt jealous as he saw his old set of boxer briefs bulging obscenely with his dad's cock and balls, and couldn't help but get a little hard at the sight, turning away even though his dick was swimming in all the extra space in his dad's underwear. He pulled on his dad's jeans and the old t-shirt his dad wore when working on his projects.
"Alright, Nate, I'm going to keep working on this here, go and have fun with my body," said Tom in a distracted voice as he started to tinker with the machine. "If you go anywhere, bring your phone."
Nate nodded and headed back upstairs, his new heavy frame making a loud sound as he went up each stair. He went up to the second floor to go to his room, but stopped at the master bedroom door. "I guess this is technically my room now," Nate thought to himself as he pushed open the door. His parents had a large king-sized bed, a walk-in closet, and a big master bathroom with a jacuuzi and nice shower. "All mine now," he thought.
He locked the door and then stripped out of his dad's simple work clothes and turned on the shower. As he waited a moment to let the water warm up, he couldn't help but look over his body in the mirror. "Dad sure has taken care of his body, even with all the science," Nate thought as he ran a hand up his sculpted abs, his hard pecs jutting over them like shelves. He lifted up his arm, checking out how hairy they were compared to his. The thick hair was matched by the furry bush around his dick, making his already small prick look somehow even more pathetic. Nate sighed, and turned away from the mirror to step into the shower. He lathered up his body using his dad's soap, feeling it run down his body, getting into the grooves between his muscles, dripping down his muscled thighs. He lathered up his dad's ass, cupping the perky and firm muscles in his hands. Nate started getting an idea and chuckled to himself as he thought, "Well, dad may have kept his dick but at least he left his ass."
He rinsed off the rest of the soap, stepped out of the shower, and dried off. Still naked, he walked over to his dad's side of the walk-in closet and went through his outfits. He grabbed his dad's work-out tank-top and a pair of gym shorts, deciding to go without underwear. After putting on the clothes, he went into his old room and grabbed his own little secret present to himself for his 18th birthday, a dildo and some lube. He strutted back to his dad's room and closed the door again. The mirror hanging on the door of the walk-in closet presented itself as a great way to watch himself.
He laid himself out on his back, propping his head up on a pillow to keep his eyes on the mirror. He made a little test moan, his dick growing hard at the sound of his dad's masculine voice sounding so needy and horny. He teased his new hole with his fingers, loosening it up as he moaned again, breathing heavily. When he felt his dad's virgin ass was loose enough, he lubed up the dildo and started teasing his hole with it. The pleasure came over his body in waves, even more than it had in his old body. His new ass stretched as he slowly pushed the dildo into his dad's ass, prostate sending out waves of pure erotic bliss. His own cock, looking out of place on this masculine body, was standing at rock hard attention. At that moment...