You manage to grow some muscle, but also...

After taking your own drink, you watched your body nervously, waiting for some sort of change. When that got boring, you ended up watching Bubble Girl instead, as she tried to find some way to keep her elastic top down over her immensely heavy chest and the adhesive bandages covering her nipples. The sight of her inability to fix the wardrobe malfunction was making you uncomfortably erect.

In fact, it felt like you were getting more erect than even you expected to. Your pants were getting uncomfortably tight, much as Bubble Girl's had a moment ago, but not in quite the same way...

Oh no...

Bubble Girl's eyes began to bulge as she watched you. "Oh..."

You adjusted your sitting position ever so slightly and asked if she noticed an effect.

"Yeah! It's huge...!"

You began to babble, planning to make some kind of explanation.

"Your bicep! I can tell that muscle's starting to build up!" she elaborated, patting her own arm to illustrate. That actually made you blush a bit. As far as you could tell, your arms hadn't increased in size at all-- you just naturally had fairly toned arms.

That said, as more time passed, you began to see the effect there, with your t-shirt growing tighter over your muscle definition. It seemed like it wasn't going to be nearly as pronounced as Bubble Girl's growth had been, thankfully, but it was good in terms of giving you some proof of concept that would cause the lady hero to set aside some of her doubts. She moved in closer, still crossing one arm over her chest, and placed one hand upon your bicep, as though hoping to feel the growth as your quirk continued to work.

You prayed she wouldn't look down. At this close proximity, you could see her huge breasts rise and fall with each of her breaths, which now came at a heightened rate. If she took a look to where you were crossing your legs in a decidedly suspicious way, she'd see that your tent was all the way pitched, with your newly enormous cock fighting to spring out from your jeans. It felt extremely uncomfortable and you were **** to free yourself, or at least find a more comfortable sitting position.

"I guess there could be something to this after all! I wonder why it worked differently between the two of us? You don't... get to decide what grows, do you?" she questioned, suddenly lowering her eyebrows again and backing up. "Did you give me boob-growth juice and keep all the muscle-growth justice for yourself?"

You shook your head quickly and reassured her that wasn't your intention.

"You know the drill then. Prove it," she grumbled, seeming suspicious now that your plan had lined up so neatly. "It seems to me like you got exactly what you wanted out of this! So if the effect is really random, unpredictable, or whatever, I should be able to drink the stuff again with a different result this time. Pour me another cup!" she demanded, taking a seat opposite from you and pouting. You couldn't blame her for being a little upset.

Doing your best to hide the frankly unsettling erection in your pants, you poured another batch into the tumbler.

"More! I want to see the full effect quickly," she continued, still holding her arms over her expanded chest.

Obeying, you emptied out additional Grow Potion into the tumbler. The liquid began to spray, then with a shhhhpppptz, the tumbler was nearly half-filled. You recognized that noise. It meant that you were nearly out of Grow Potion for the day. No more would come out until tomorrow unless you found time to fit in a good nap.

But also... was it really safe for her to drink this much? You really hoped it'd have a less embarrassing effect on her this time. Or did you? It was hard to decide.

Before you could caution her to start with just half the cup or something of that nature, she grabbed the tumbler from you and drank heavily, until she'd used up downed the entire thing without stopping. You began to wonder if she might be the type who likes to grab a few drinks when she's off work.

She wiped her mouth with her glove, set the cup back down, then held one hand up to her mouth. You thought she might be stifling a burp. "Ahem! Now, if this thing is really fair to men and women alike, we'll see if I manage to actually grow in a good way this time. Not that having big boobs like this is bad. I mean, from a publicity standpoint, there could be certain advantages..."

Your raised an eyebrow.

"I-I'm just trying to speak objectively. Obviously, I don't want to have them this huge, but it's just... worth talking about the potential benefits," she pouted, crossing her arms more for the sake of huffing irritably than hiding her boobs this time.

Benefits, huh? You couldn't help but stare, imagining what it would feel like to touch those. They were so large, you thought they might be bigger than your hands could grip at this point.

But you didn't need them any larger! What you needed was some other proof of concept! You prayed to whatever god had decided it was a good idea to give you such a nonsensical quirk that he would find it in his heart to stop being mischievous for now and let you get this development grant!