"Let me show you what I can do..." Ty purred, running his fingers across Gavin's thick chest. The taller boy's bodyfat slowly began to recede, the pudgy aspect of his physique lessening as the fat burned away. At the same time, muscle blossomed under the skin, rushing to fill the empty spaces. Ty dug his fingers into Gavin's pecs, pleased to feel the muscle grow beneath them. The larger man let out a soft grunt of surprise, feeling his muscles grow larger and firmer. He took deep breaths as his growing chest forced back Ty's fingers, his muscles seeming to swell more and more each time he breathed in.
"Going to be so sexy..." Ty purred, giving Gavin's nipples a teasing tweak. The growing muscleman's gasp of shock made Ty grin, and he leaned in to give each nub a few slow licks.
"Fuck man, how big are you making me?" Gavin asked, his voice cracking as it deepened.
Ty chuckled. "Pretty big, Gavin. Not as big as Nick, of course. But close enough..." Ty reached down and gripped Gavin's dick. Between the excitement of growing and Ty's attentions to Gavin's chest, the larger male had become fully erect, his dick reaching its full seven-inch size. Ty gave it a few appreciative strokes, and began to tug on it. Gavin's face went red, but he couldn't stop it--it felt too good! As Ty pulled, the rod lengthened and thickened, getting bigger and bigger until it was a 12-inch monster. Ty squeezed the base of the thick shaft with both hands, and Gavin's balls trembled, then doubled in size.
Pleased with how Gavin was coming along, Ty stepped back to admire his handiwork. Gavin's muscles were growing nicely, and his cock and balls looked disproportionately large, even on his expanding body. Ty focused and rectified that error: Gavin's height shot up until he was six-foot-four, and his muscles bloated all over, until he was 350 pounds of rock-solid, beastly brawn. His bodyfat was quite low, making every muscle cut and striated, showing off a number of thick veins.
Gavin let out a bellow of ecstasy as he grew to his final form, loving the size and power of his huge new body. He'd spent years ogling the hunks in comic books and on the internet, and had started working out to try and look more like them. But despite all his fantasies about being a huge muscleman, he'd never imagined it would actually happen. But whatever juice Ty had, it had given him the body of his dreams in minutes!
"This is incredible!" Gavin enthused, running over to Ty and wrapping his huge arms around him in a grateful hug. "How can I ever thank you?"
Ty smirked as he nuzzled against the larger man's thick chest. "Oh, don't worry, I have ideas, Gavin. Last night I dreamed about having a three-way with Nick and another huge stud. It was really hot! Guess what, Gavin, you're that other stud!"
Gavin nearly choked on his own tongue. His warm embrace froze, his huge body tensing up. He released Ty and stepped back. "Th-three-way? What the hell do you mean?" he demanded.
Ty laughed wickedly. "I want you and Nick to both fuck me at the same time! I can't wait to have two big-dicked musclemen to play with!"
"I- I don't know about that," Gavin stammered. He was still a virgin, and was very uncertain about Ty's proposition.
Ty sighed in annoyance. A huge mirror appeared in front of Gavin, showing him his massive new body: tall, heavily-muscled, lean, and seriously well-hung. A second image appeared: Gavin's old body. It showed some promise, but was almost pathetic next to what Gavin had become.
"I'll make it simple," Ty said, his voice sounding light and airy, but with a definite hint of malice to it, "You can keep your new body, if you join Nick and me for hot three-ways, whenever I ask. Or, you can go back to being your old self. And I can guarantee you'll never get this body through hard work. Not even hard work and steroids. I can guarantee it."
Gavin gulped. He heard the threat in Ty's ultimatum: if he didn't agree, not only would he lose his amazing new body, but it sounded like Ty would curse him to always be stuck in his old one! In light of that, there was really no choice at all, the way that Gavin saw it.
"I- I-... okay," he said at last in his deep new voice. "I agree," he sighed.