Jen, her boyfriend Clint and the man screwing her senseless, Jim, all worked in the advanced research division of PharmTech. Clint headed the division working on sports performance. Jim was in charge of research into drugs to enhance sexual performance. Jen was no fool. She knew both were insanely competitive, and both had obviously secretted some potential product. Clint said he had joined a gym, but that hardly explained gaining 100 pounds of ripped muscle, pushing his weight above 320 with 4% bodyfat. And now she was experiencing Jim's "Mr. Fantastic".

Jim never had problems getting fucked. He started working out at 13. He entered his first competition at 17, and won the national teen championships twice at 18 and 19, coming in second when he was 17. His 56 inch chest, 21 inch arms, ripped abs and 31 inch thighs turned on men and women alike, and Jim had taken advantage of it. He loved the looks on their faces as he slowly stripped off his clothes, twisting and flexing his muscles. He would start with his shirt, unbuttoning from the top to reveal his rounded pecs, perfectly formed. He'd bounce them, then flex hard showing striations in the muscle, thick veins feeding life-giving blood his hurculean chest, and a deep ripple between his upper pec shelf and his lower pecs. He'd then lift his shirt, flexing his brick-like abs. After he finished unbuttoning his shirt, he'd twist, flaring his wing-like back as he pulled the shirt over bowling-ball sized delts. His arms now free, he'd flex his 21 inch guns, bringing the huge bicep to his lips and kissing them. "Fucking huge," he'd whisper, offering his pumped gun to his partner for them to worship. Most jumped at the chance, and some heavy kissing would ensue. Often, they'd rip Jim's clothes off and the fucking would begin. Some, like Jen, refused the offer. "Clint's are 29 and growing," she said. Jim pressed on. He flexed his thigh, showing how the denim needed to stretch but still reveal thick cords of muscle in his quads. He unbuttoned his pants, rubbing his hand over hard abs with no bodyfat. While flexing, he forced blood into his cock, keeping it soft but forcing it larger to make a substantial bulge. Lowering his pants was another opportunity to flex his wide, thick back. He'd pause, struggling to get the tight fabric over his diamond-like calves. Finally, he'd stand, put one foot forward and shake his massive quads before flexing into a hardened landscape of ripped muscle and thick veins.

Jen yawned. "Ya know how skinny you look compared to Clint?" she asked.

Jim grimaced. He knew. That was why she was there. Jim was use to being the number one muscle god. He knew Clint had a secret. Hell, no one got that big that fast without something. He just needed to convince Jen to get it for him. Jim's secret weapon was "Mr. Fantastic."

The Fantasic project, as he thought of it, was an accident. Two of his research teams had interesting ideas. One was a pharmaceutical that enhanced the male organ. It worked like viagra, but also lengthened and thickened the penis. The second group divised a nutriceutical that seemed to have an effect on women. When men took it, they seemed to be able to consciously control when and how intense their partner orgasmed. Both projects were killed by the company lawyers who thought them too risky, but Jim was intrigued. What if you combined the two. Computer simulations were encouraging. They predicted that a man could control blood flow and pressure in his member. According to simulations, the control was directly proportional to the fitness, strength and muscularity of the man. Jim had to try it. With his trophy-winning physique and gym-trained strength, Jim was the perfect test subject. In the lab, he made gallons of the formula and spirited them home. The formula worked better than predicted.

Jim lowered his briefs, exposing his soft 10 inches and softball-sized sack. Jen gasped. "Clint brags about his hard nine." Jim lifted his cock in an arrogant display. "That's tiny compared to what Mr. Fantastic can do." Jim strutted over to Jen, grabbed her hand and moved it to his meat.

"It's so big and heavy! You'll rip me apart!" she said.

Jim could feel her quiver with desire. "Don't worry about that," he reassured her. He lifted Jen up and carried her to his bed. Putting her down gently, he began to kiss her, removing her clothes as he worshipped her soft, feminine body. He moved his mouth to hers as he gently stroked her breasts and pressed his body onto hers. He willed his dick hard at a monsterous 15 inches and rubbed it hard into her cunt. He could feel her juices beginning to flow. He willed his cock thicker to a nine inch circunference. He moved her hand to it. Jen tried to grab it, but it was too thick for her small hand. Jim smiled and bit at the nape of her neck, causing her to shudder. "Ready?"

"Too big..." she whispered.

"Trust me." Jim pulled her hand away and willed himself smaller. 5 inches by 1 inch -- a small pencil dick that could slip into her easily. She cooed as he ground his powerful body against her clit, then willed himself longer and thicker, stopping at a normal 6 by 3 inch size.

Jen giggled. "That was so gentle," she said.

Jim kissed her deeply as he slowly pulled out and willed himself to a large nine by six, which he thrust quickly into her. "That feel familiar?" he chuckled, knowing that Clint had always been a showoff, even before his recent transformation, and was particularly proud of his size.

"Don't know why they gave you sex and me athletics," he had joked when they were assigned projects. "You're the one with the trophy-winning body, but I'm the one with the cock that drives women insane!" Clint grabbed his crotch through his pants and hefted it up, laughing as he walked away.

Jim grinned at the memory. He commanded his cock to grow and thicken by another inch as thrust hard.

Jen screamed as Jim felt her chute tighten around his steely-hard thickness, her walls throbbing as her juices squirted over his organ, lubricating its way as it pushed deeper into her. Jim withdrew slowly, allowing her to experience every inch of Mr. Fantastic before attacking her G-spot a second time.

For 15 minutes, Jim has kept Jen in orgasmic bliss. He could feel her heart racing. She was babbling incoherently, "so big...", "yes", "oh god...", "such a man", "more...", "never before..." Jim's control of Mr. Fantastic had the desired effect. Jen clawed at Jim's massive chest, her eyes bleery, "so strong... please.... cum... wanna feel.... oooohhhhh..."

Jim thickened Mr Fantastic to nearly ten inches, filling Jen up. He then began to sqirt his juices, erupting for nearly a minute. When he finished, he slowly pulled out and lay next to her.

Jen didn't move. Her body was covered with sweat, and she was breathing heavily. Jim rolled over and kissed her. She didn't react.

Jim smiled. "Passed out, huh? When did fucking Clint ever do that to you." Jim looked at Mr. Fantastic and flexed, willing himself hard. His cock responded by growing longer and longer, thicker and fatter. Mr. Fantastic grew between Jim' pillow-like pecs, and he squeezed and flexed them around the fat pipe. Jim strained to grow as long and fat as possible, eighteen-plus inches and aver a foot around. He moved his mouth to his dick and kissed it. "Fucking amazing," he said as he blew himself and drank a massive load of his own cum.

Jen began to move, and Jim let his cock return to normal size.

"What happened?" Jen whispered.

"You need to ask," Jim said, kissing her.

"Oh Jim, you were amazing! I never..."

"Glad you liked it. So, guess I won that challenge?" he said impishly.

Jen turned away. She started to cry. "Oh Jim, what have we done. Clint's body is amazing, and he is great in bed, but..."

"He can't rock your world like Mr. Fantastic, right?"

She nodded and weeped harder.

"You like muscles, huh? I saw how you use to look at me before Clint," Jim paused, searching for the word, "changed."

Jen turned and looked at him. "Jim, I didn't think you noticed!"

"Of course I noticed," he said, kissing her, and deciding to go for the kill. "Who couldn't notice a bombshell like you." Jen smiled. "But I also noticed that Clint gained a lot of muscle real fast. Too fast."

"He's still getting bigger too," Jen admitted.

"You know something?" Jim whispered.

Jen nodded. "I'm not suppose to, but I've seen a few things. Clint takes this supplement. He also has vials of testosterone and HGH in his 'fridge. And..." Jen stopped.

"And?" Jim asked, waiting for Jen.

"I saw some papers. I didn't understand them..."

"But I would?"

Jen nodded.

"Ya know, if Jim got that big, I could get fucking huge! Would you like that?" Jim asked.

"Stop it Jim! I'm not stupid. You're trying to use me." Jen pushed away from him. "Yes, I would like it. Clint's a nice guy, but you aren't the only using people. I admit it. He's a great fuck."

"But I'm better. Think how good if I were as big, or bigger, than..."

"I'll get you a copy of the stuff and a sample of the supplement, but there's a catch," she inerrupted.

"Sex?"

"That and something else. My brother Mark. He's 13 and kinda small. He keeps getting beat up at school, and can't get a girlfriend to save his life. You have to share the formula with him. ALL the formulas," Jen said knowingly.

Jim laughed, knowing he didn't really have a choice. "Now who is using whom?" He kissed the back of her neck. "You get me the stuff and I'll help the kid. Deal?"

"Deal," she agreed, turning to Jim, kissing him and grabbing Mr. Fantastic and stroking him into hardness once again. •