*Just a few more seconds, then it is finally complete!* John thought to himself. *I've had enough of the genetic lottery. Screw Dad. Screw Beth. It's my turn now!*
John gave the light brown liquid in the beaker a confident look before he grabbed it. He swirled it around a bit before slowly guiding the beaker towards his mouth, all to eager to prove to everyone that he was more than anyone has ever thought. So much more. Just as the cold glass touched his lower lip, the beaker was forcefully pulled out of his hand, much to his surprise. If only he had turned around sooner.
As he did so now, he saw Beth holding the priceless efforts of his masterplan in her strong, yet feminine hand, looking at him with the same arrogant eyes and that bratty, smug smile. John was getting angry really quick again.
"What's this, brother? Not only did mom allow you to have your 'oh so serious lab' down here, but now you're also drinking energy drinks out of these? That's just weird, John!" she exclaimed, laughing as her brother's face turned red through anger.
"Shut up, Beth! This is none of your business. Now give me back my beaker!" John ordered, his hand wide open and awaiting the compound. But Beth simply slapped his wrist, indicating how little she cared about it.
"Right, a beaker! That's what it's called! Why should I? Can't survive five minutes without this junk? Maybe I want it for myself, ever thought of that?" Beth was as chilled as ever, but John's face went from red to pale in an instant. He had to stop her!
"W-Why would you? You've never liked them one bit, so why now? Give it back to me!"
"Or else, what? Are you going to tell mom that I stole it from you?"
"That's not it, I just want to-"
"So it won't be a problem! Besides, you can probably recreate some of their formulas, can't you, genius?"
With that she gulped the entire compound down in a few gulps. It wasn't that much, so she didn't notice the taste until after she was done with it.
"Ugh, what kind of flavor is THIS supposed to be? Loser lychee?"
Then it hit her. One part after another, her entire body began to feel weird and started to tingle. As she looked at her puny brother she noticed the expression of utter shock. This couldn't be because of some sugar drink! Beth started to panic internally, not knowing what's happening to her. It wasn't until her right upper arm started warming up to the point that it felt like it was a few degrees away from burning. Her panic quickly changed to wonder as she saw her tight, yet small biceps slowly bump up in size. She held her arm up next to her to get a closer look.
Her fitness-level biceps became more noticable, now easily reaching athletic levels of size. By now it began to feel hotter as the last steps of the growth were concluding, leaving her with semi-flexed mounds the size of a baseball. It looked very defined and hard already. She gave it a quick flex, causing the ball to get slightly larger as it even harder. She was starting to grin, but was immediately interrupted by her other arm, undergoing the same kind of growth. She too flexed it and was amazed by them.
She looked back at John. Now she knew why he was acting to weird. This wasn't an energy drink, but rather some kind of muscle growth formula. Now that she saw it with her own eyes, she knew she was going to enjoy the rest and rub it into her brother's face as best as she could.
Next she felt a familiar heat building up in her pecs. While she didn't feel them expanding all that much in size, she could definitely feel them getting much denser and stronger. Right after that, her midriff heated up and involuntarily flexed like crazy. As it did, her faint sixpack got more and more defined as each block grew in size until they looked like the most impressive abs she has seen with her own eyes yet. Playfully, she reached for them and poked them in their unflexed state. Even then they were rock-hard and shapely.
Next the feeling spreaded all throughout her hips, ass and legs. As her hips flared out a bit, her cute, toned butt pushed outwards as the skin stretched tightly over the hard cheeks. Whereas her thighs have been athletic before, they now looked massive. They were still feminine as can be, but showed vast amounts of strength hidden within them. Even her calves got a good pump as they stuck out behind her lower leg.
Lastly, her back went from soft to chiseled, giving her body the last touch, leaving her as one of the most athletic and defined woman known to mankind.
"Say, brother, could it be that this wasn't actually a regular drink?" she said sarcastically, her smug smile looking almost evil to him.
"I-I don't know. If you want we-"
"I think you know all too well what this stuff was. And you wanted to drink it yourself to, what, get revenge on me? Looks like you've failed again, as you always do!" She inspected her body once again, still joyful that literal years of hard workout just casually piled onto her body from one small beaker of liquid. She flexed her abs and her left arm. "God, you don't know how good this feels! And you probably never will. This is so typical of you. Always wanting to cheat and never put in the work. Good thing I stopped you before it was too late!"
She walked over to her weights she'd used just a couple of minutes ago. The one she was using had her struggling quite a bit, so she decided to test her strength again. Before her growth, this was almost the maximum she could do, but now these felt... easy. Shockingly easy. She wasn't even sure if these were real weights anymore or those fake ones some people online used. She curled it a few more times, always getting faster as she couldn't believe her incredible fortune. She always wanted to be as strong as her dad, and now she had a body more than capable of reaching that goal.
Meanwhile, John rapidly turned around after watching a few seconds of her impressive feat, trying to hide some of his notes containing hints as to how the compound can be replicated. He had to hide them as best as he could before Beth got her hands on them!