Forget say, you have to stop her!

You throw yourself out of the bed, staggering on legs that are stronger and longer than you're used to but slightly weak from the recent orgasm, and push yourself off the dresser and toward your sister just as she rushes out the door.

Your body is strange and unfamiliar to you, but it's also strong and fast, and your first bounding step rip your panties apart with a violent tearing sound. It only takes a couple bounding steps to tackle Amanda from behind before she can get too far, clapping a hand over her mouth just as she draws in a breath to scream.

"Amanda!" you hiss in her ear. "Calm down, it's me! Calm... down!"

Somehow this fails to work, and her body heaves and bucks underneath you. Amanda's six years older than you, normally two inches taller and much more toned, but as you tighten your grip on her, shifting your body to pin her more firmly, you realize that your new body has five inches on her, and maybe fifty pounds. She has no chance of getting away, wiggle and squirm however she might...

...oh. Oh fuck, why is your penis still so sensitive?

Amanda's in her usual sleepwear, just a cotton t-shirt and some panties. Plain, simple white panties, panties that don't quite cover her round ass, and which ride into it as you feel your cock twitching, suddenly, twitching and growing, growing and pressing, pressing between your sister's thighs...