Kylie and her twin sister Jessica grew up together as thick and thieves; they hung out in the same social groups as kids. As they both turned 18, they drifted apart.

Their personalities could not be further from each other.

Kylie was the short booty skirt and bikini party girl, and Jessica was the trousers-wearing bookworm.

Kylie wanted to explore herself and not settle down. Jessica dated the first guy who kissed her.

Kylie had not spoken to her sister in a while and was surprised when Jessica asked her to come to her apartment. They started with small talk, but Kylie could sense Jessica had something on her mind; once Jessica told Kylie of her plan, Kylie felt her cheeks burning as she blushed.

Jessica's boyfriend, Mark, had been pushing her to get kinkier in the bedroom, and with her boyfriend's 21st birthday coming up, she wanted to do something special for him.

She disclosed to Kylie her cuckquean kink and her voyeuristic nature.

Kylie refused initially, but after some convincing and calling in favours, she relented and reluctantly agreed to the stupid plan.

The plan was like something out of a porn film, and she wanted Kylie to take her place and let Mark use her in any way he saw fit. Kylie felt her heart pounding as Jessica rattled off some of Mark's fantasies.

Kylie spent the next week thinking about the plan, the days growing longer the closer they came to Mark's birthday.

Kylie had slipped into Jessica's house when Mark was at work and started to get ready, her hands trembling as she slid on the new black set of lingerie. Her brunette hair framed her face, and her blue eyes showed her anxiety but also her lust, her arousal at the situation.

Kylie left the bedroom and took her place on her sister's bed, and waited for Mark.

Each passing second felt like an hour, her heart starting to pound against her chest as she heard Mark making his way to the bedroom; a small tingle ran down her slit as the door opened and they locked eyes.

She couldn't believe she was going to do this…but she cleared her throat and whispered.."Happy birthday, Baby" as her cheeks turned red

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**A.N. Looking for some advice on how to improve this prompt**