Lina

Stacy tried to make noise, screaming into her stuffed mouth and writhing on the bed to try to drag it across the room, but little came of it.

Help me! Find me and get me out of here! Whoever it is, untie me! Release me! Please, someone hear me! Listen! Come to me! See me! Here, naked, prone, available. Look at me. Desire me. Crave me. Fuck me. Take me! Inside of you! Let me claim you! Let me show you what you need! Be mine!

Her cock swelled but still she struggled. Stacy felt like she was in control aside from the unnatural arousal.

"Jeeze, calm down. I didn't take that long." Stacy knew she should feel despair at her sister's return, but her mind was filled frustration and arousal. She wanted to fuck Lina so hard that even someone that perverted would refuse.

Lina sighed at her sister's face, "Look, I went as fast as I could, but something came up." Lina started petting her sister's dick, forcing her anger to subside a bit, "I think you'll like it, but you'll have to let Stacy out for a little bit." Lina's grip tightened as she started bending Stacy's dick down. It grew more uncomfortable till it was outright painful. Stacy wimpered as her hard penis was bent all the way back to her more feminine organs. Both she and the parasite wished to fight back, but there was little either could do with their limbs bound and Lina's firm grip on the member. Stacy couldn't tell which of them was screaming more as one sex organ was **** into the other.

"So," Lina reaches up to take out the gag, "Which one are you?"

Stacy took a sharp inhale, but her sister's hand slapped down over her mouth before she could scream. "Well, guess that's my answer." Lina shrugged as she replaced the gag. "Seriously, sis, you got to stop resisting every little thing. These things will be your friend, if you let them."

With that, Lina began to strip her school uniform. She worked her way down, drawing closer as she unbuttoned her shirt. Her sister's cleavage seemed to grow before Stacy's eye as Lina leaned over her face before spilling her breasts onto Stacy's face.

Stacy's lust could only grow. She started wriggling her hips trying to grind her own cock against the walls of her vagina.

Lina giggled "Look at you, sis. Finally in control, and you're fucking yourself. Though, I doubt you're getting much out of this, are you?"

At Stacy's silence, Lina twisted a nipple, "Answer,"

Stacy screamed through the gag as she shook her head.

"Good girl," Lina traced circles around the now sore and erect nipple, "How about I help you feel good, would you like that?"

Stacy could feel her sister's fingers tightening around her sensitive nub. She desperately nodded to avoid the pain.

"That's a good girl," Lina cooed as she leaned in for a kiss, though, with Stacy's mouth blocked, she kissed the tip of her sister's nose instead.

With Lina so close, Stacy couldn't tell what was happening below. She could tell Lina's hands were moving around their crotches, but it didn't amount to anything pleasurable.

Until something prodded at her beneath her penis.

"Turns out, birth control doesn't work against these things." Lina explained as she slammed her cock deep in her sister.

Lina fucked hard and fast. With how close Stacy was already, she couldn't last long.

Or at least, she wouldn't last long if she could cum. With her dick folded back over itself, Stacy couldn't ejaculate, and by some synchronicity, this prevented any other release.

It didn't matter to Lina; she just kept mauling her sister's body without care. She'd dig her nails into Stacy's breasts and try to rip them off in a corkskrew motion. She'd bite at her ears, and lick at her neck. And when that started to bore her, Lina tried to see how much of her hand she could fit in Stacy's ass. All the while, her cock drilled at her sister's cunt, forcing more pleasure with nowhere to go.

Lina didn't have that problem. She could, and did, cum several times. Seems those **** she picked up from the pharmacy got repurposed. Stacy was acutely aware of her sisters, of another parasite, breeding her by ****. The thought spread through her mind, cementing this moment in her mind. This was swiftly becoming more than a fact. This relationship, this power dynamic, was becoming truth.

"You look about ready." Lina leans forward and puts her hands on the gag. "Be a good girl and stay quiet."

With the gag removed, Stacy keeps her mouth closed, but can't help her noisy moans.

"You belong to me now. All of you, head to toe. Whether it Stacy or the dick moving your body, I control you."