The serum works a little too well

At first nothing happens. The silence in the room gets heavier and heavier, until Emily sighs. "I guess I made some mistakes. Sorry for making you come all this way for nothing, Doug. It was really kind of y..." In that moment she drops to her knees and clutches her stomach. "Oh fuck!" She shouts, gritting her teeth, eyes closed. "God that hurts!"

Not knowing what to do, you watch as Emily starts to change. It is subtle at first, her clothes slowly tensing up, her sleeves and pants climbing up her limbs, her shirt getting tighter. Her grunts of pain slowly turn into moans of pleasure, she lets go of her stomach and sits down on the floor. "Oh fuck" she says again, but this time her voice is husky and charged with lust. Her cock is starting to get hard under her clothes, and it is pulsing bigger.

You can actually see it happen now! Her growth is speeding up! It comes in waves, like breathing, her legs stretching further, her shirt getting tighter, her bulge bigger. And it's not just her height, her ass and boobs are growing too, and you start to see a hint of abs on her now exposed belly.

"God, this feels so..." she says, moaning and rubbing her cock over her clothes, unable to resist. "It feels so fucking good, like stretching but so intense and... my whole body is tingling." She looks at you with pure lust in her eyes, her mouth open and a tiny bit of drool leaking out of her lips. She forces herself to stand up, her legs wobbling, and she lunges towards you. Her face is now a mere inch from yours and you realize that you are looking at her in the eyes, but only for a brief moment, before she grows even taller.

She closes her lips against yours, her tongue invading your mouth. She pins you against the wall, her growing body rubbing against yours. You can feel the muscles in her arms growing tougher and bigger, her boobs rubbing against you, softer, bigger, and getting higher. Her bulge too rubs against your own, then your stomach, getting worryingly big.

"I-I'm sorry, I'm not like other futas, I don't want to take advantage of you" she manages to say, tearing herself away from you, "but it feels so good! I cannot help it" She adds, moaning again as another surge of growth makes her shoot way past your height. Your face is buried in her chest, your entire vision is filled with her soft wonderful boobs. "Please help me!" she pleads, grinding herself against you with increasing fervor.