A strap on dildo.

You gasp, the sound only slightly muffled by the hand you clap over your lips as you stare at the object in Mira's hand. The dildo's shaft is long and thick and made from shiny black rubber. Realistic ridged veins stand out on it's surface and it's bulbous flared tip is the size of a large plum. Webbing straps are attached to a pad at the base of the fake cock with a second, smaller shaft curving inward from the pad.

"Mira?" You say softly, looking up to see the mischeivious glint in your stepsister's eyes.

"You must have guessed little sister that you're not the first girl to lie on that bed with me." Mira tells you with a grin.

"Well yeah, I figured that much." You admit. "Sometimes I'd hear you and your friends giggling and moaning through the wall between our rooms and I'd imagine you two together."

"Hmmm, bet you wanked your little cock, lying there listening didn't you?" Mira asks.

Your ashamed and flushed red face answers that even before you give a guilty nod. Many a night you had jerked yourself off imagining what Mira might be doing with her friends when they slept over. Even in your fantasies though, there had been nothing like the strap on sex toy Mira is now idly fondling as she teases you. You feel fear and excitement whenever you look at the big black dildo in her hands and Mira can obviously read your conflicted emotions in your expression.

Never taking her eyes from you Mira steps into the strap on's harness and slides the toy up her legs. Her fingers rub her pussy for a moment and come away glistening and wet. Mira giggles when she looks at her fingers.

"Look what you're doing for me little sister." Mira laughs. "Dripping wet already just thinking about fucking you."

Mira says those last two words loudly and slowly, "FUCKING YOU". If she'd deliberately used the crude term to get a reaction you don't disappoint her. Your new feminine body shivers and trembles and you look up quickly from the toy to Mira's face.

"Will you be gentle with me Mira?" You ask. Your soft, girlish voice breaking and stuttering slightly with the fierce and conflicting emotions you are feeling.

"Oh no, not at all." Mira says with a shake of her head.

Your stepsister rubs the smaller inward shaft once or twice up and down the cleft of her pussy then slides it smoothly into herself. She pulls the webbing straps to tighten the harness and then puts her hands on her hips so you can stare mesmerised at the big black toy now sprouting from her crotch. It is nearly twice the length of your own cock, which you had always thought of as being only slightly smaller than average. It's girth too is much more than your now vanished natural cock.

"In fact I'm going to fuck you harder than I've ever fucked my girlfriends." Mira informs you. "And when I'm done you'll be glad I did."