Her tits explode at dinner

You spend the next hour in a nervous, horny daze. First you clean up the kitchen, then whack off in the sink, then clean it up again. That's about when your mother comes in to start making dinner, so you make an escape to your room.

Pulling out the Upgra-D container, you try to get some more information about what's going to happen to your sister. The warnings are all infuriatingly vague, however: all you find out is that she's going to experience "rapid, **** swelling." You've definitely given her too much... More than twice the recommended weekly dose, in fact.

Soon Mom calls everybody to the dining room. On your way downstairs you bump into your sister, still damp from the shower. Julie's changed into a pair of sweat pants and a loose, flowing red blouse, so you can't get too much of a read on whether her chest has grown yet. The **** you took haven't worn off yet, though, so just seeing her is enough to get you rock-hard. Turning away to hide the bulge in your pants, you rush off to dinner.

You and Julie are the last to arrive, sitting across from one another while your father and mother get settled in. Greg had a hard day working from home, apparently; he's ranting about a client while Christine nods understandingly and serves out the pasta.

As you all begin eating, you take another look at your sister. She keeps fidgeting with her top, adjusting and re-adjusting the soft material with a confused expression on her face. One of these small motions pulls the fabric against her nipple, clearly outlining the firm nub. When that happens she shoots upright and gasps, as though that tiny bit of contact sent shivers down her spine.

The moment of tightness also lets you get a clearer look at the size of her breasts: it's hard to tell, but you think they've grown just a little bit since before her shower. Seeing that is enough to make your cock even harder, and then it's your turn to shiver as your ultra-sensitive shaft rubs against the inside of your pants.

"Guh--Uh, g-good pasta, Mom," you grunt.

"Thanks Sweetie," she says absentmindedly, before turning back to her conversation with Dad.

It seems as though they're too busy to notice Julie, who's staring down at the table and breathing heavily. Her top is just hanging loose now, but with every gasping breath it seems to be getting tighter. Soon both her nipples are pushing into it, then it rounds out further, then some cleavage appears in the neckline...

Unable to hold back, you reach into your fly and fish out your erection. You begin to stroke it slowly, eyes glued to your sister's growing tits. She's leaning back now, eyes closed and hands clenched around her knife and fork.

"Julie?" Mom seems to have noticed, and she's looking worried. "What's wrong?"

"I... I'm okay," Julie replies. She's only growing faster, and her formerly-loose top is pulled tight against her round, perky breasts. "It's just--I feel--"

"Y-your chest," Dad stammers, immediately picking up on her increased size. "What the hell are you wearing, young lady? Is that a push-up bra?"

"She's not wearing a bra at all," Mom gasps, leaning closer. "Julie, what did you do?"

"Nothing! I don't know!"

You continue jerking off under the table; it's not as though anybody's looking at you. Your sister is a sight to behold, the hem of her top lifting off her navel even as her cleavage grows deeper. In fact, it's starting to look uncomfortable: her tits are bulging out of the neckline, straining against the flimsy material.

In your "altered" state, you're finding it harder and harder to keep your composure. Seeing your sister's tits ballooning like this, all because you **** her... It's too much to handle.

"Here, let me help," you say, reaching across the table and grabbing the seam of her top. Before anyone can react, you give it a sharp tug. It was already weakened, so that's enough to rip it open from top to bottom.

"John! What the--" Your father looks furious for a moment, then falters as Julie lets out a sigh of relief. But when everybody sees your exposed dick flop onto the table, fully-erect and leaking pre-cum everywhere, your family all starts yelling at once.

You don't listen to a word of it, though. You're too busy staring at your sister's naked breasts... Her perfect, massive breasts. After a few seconds, you speak quietly:

"...She's a D-cup..."

Nobody hears you, so you raise your voice and try again.

"She's a D-cup, now. At least."

Everyone pauses, and their eyes go wide. Your sister looks especially shocked, of course. "That's--"

Before she can finish, you jump up onto the table. Both your meal and your sister's go flying as you move across it, shuffling on your knees while still stroking your cock.

"John... John!" Someone is trying to get your attention, but you can't even tell who it is. You have tunnel-vision at this point; nothing matters other than your sister's tits. Your tits.