Mark stared at his little cousin's enormous biceps threatening to burst out of his sleeves. He had never seen such large muscles on anyone before, much less a 10-year old kid.
Andrew didn't notice Mark's reaction as he was completely focused on flexing his arms back and forth. He tried pulled his sleeves back, but the t-shirt became stuck as it strained to wrap around his shoulder muscles.
"Haha, I dunno if I can even take my shirt off. I'm so big!" Andrew spread his hands over his chest that pushed his shirt outwards. He felt how wide and full they felt, packed full with muscle. Andrew looked down, and was surprised that his shirt didn't outline the abs anymore because the pecs stretched the fabric outward from his thin waist.
Andrew lifted his shirt and gawked at how his 6-pack seemed even harder. He grinned and flexed them by hunching forward, like the way bodybuilders did it on TV. The cobblestone bricks of muscle popped out and pushed against each other in a way that made Andrew feel like he could take on anything.
His stomach suddenly grumbled and he laughed. "I'm a growing boy and I need to EAT!"
Mark picked up his jaw from the floor and remembered his manners as a host. "Well, we have some leftover chicken and broccoli from last night. Would you like some?"
"Yea!"
Mark heated up the dish while eyeing his muscle stud cousin. He glanced back at the box of vials and stared at the opened bottle. If one vial could make a kid as strong and muscular as an ametuer bodybuilder, what else could that package contain? He wanted to check out the other ones so badly, grimly accepting that Andrew downed the entire muscle vial. He didn't know about it's magical refilling properties, but maybe there are some other things he might like.
But he hesitated. What if some of the vials had an opposite effect, or worse, made him ugly! Plus, he didn't dare make Andrew wait longer than he had to. That kid could probably beat him in a wrestling match if he tried. Mark wasn't scrawny or anything, but his lithe frame left much to be desired. The only advantage he had over Andrew was his height and good looks. He would have to wait... for now.
Mark set the plate down, and Andrew dove into the chicken ravenously. "Mmm.. This is as delicious as it was last night," he said between bites. The short muscle kid all but devoured his food and held the plate up to Mark. "More, please!"
"You- you want more? But we ate lunch an hour ago and you just had twice the amount from last night!"
"So? I gotta feed these puppies, don't I?" Andrew brought both arms up into a double biceps pose and winked. The cute dimples from his smile betrayed his tough-guy look, and Mark could gulped as he felt hot from his cousin's "little" display. Andrew's biceps suddenly seemed even rounder, more firm as he kept them flexed. His smirk contorted into discomfort as if he was straining to keep his pose.
"Urgghnn... It's- it's happening again. I said I want MORE." Andrew grunted. His voice was still high and squeaky, but there was something in his tone that suggested he had power and authority over Mark. And Mark melted at the sound of his younger cousin's demanding outburst.
Despite Mark's urge to grab another helping of chicken, he stayed glued to his spot. His eyes bulged out of their sockets as he witnessed what was happening before him. "Andy... Look. You're growing again."
"I know. Unhh. I can FEEL your food making me bigger!" Andrew glanced at his pulsing biceps, then back at his awed cousin. Mark was incredulous. Andrew wasn't even moving his arm, and yet the peaks of both biceps rose and hardened as if he was flexing harder.
"And don't-" he brought both arms down and stood up, the dinner table and chair pushing away effortlessly to make room for his growing body. "-call me-" he continued as he brought both arms into a crab pose, "Andy." And he flexed. His flimsy t-shirt tore down his back, and the two heard more ripping noises from Andrew's sleeves as the shoulders bulged and grew outward like bowling balls were packed under his skin. Andrew's traps rose and revealed more of its presence as the shirt stretched away on opposite sides. His face was red with determination, lips pursed and eyes glaring back at Mark. The older cousin saw just how much of Andrew's torso grew as the glorious chest muscles bunched forward like two fluffed pillows, each with a perky nipple that poked against the already-strained fabric. The shirt lifted up and revealed the bottom row of thick, hard abdominals surrounded by carved obliques that altogether formed a V-shaped waist.
Louder ripping noises erupted from below as the skinny jeans that were packed with lean muscles from before were now bursting through and creating several tears. The denim looked as if it was still struggling to stay together as several strands were stretched to their limits, but Andrew's monstrous thighs had other plans. His calves burst out from behind his legs and were thick enough around that Mark didn't think he could wrap both hands around them.
Shit, Mark was drooling at this sight. He finally broke out of his reverie when he looked back up to Andrew's eyes piercing into his. "Oh- uh, sorry. I thought you liked that nickname. I'll get you some more chicken right away. It's a good thing I made plenty extra." Mark laughed to ease the tension, and it seemed to work as Andrew relaxed his pose.
The shirt fell away and Mark wasn't sure he registered whatever Andrew said next. It was probably something along the lines of "I never really liked 'Andy'. It made me feel like a little kid. But now that I'm big and strong, you have to call me Andrew." He flexed one arm at Mark to prove his point.
"Heh, it's probably bigger than all your muscles put together," he gloated. His biceps was swelling larger and larger as if he was still growing. The stretch marks on the smooth skin showed just how much had changed in the past hour.
"And keep those plates coming. After all, I'm-"
Mark finished his thought together "a growing boy."