Sarah sets some ground rules.

When Adam woke up from a dreamless sleep, he was greeted by the sight of his sister standing in front of his bed, dressed in a tight top and skinny jeans that gave her a noticeable bulge. A bulge that made his mouth water and his pussy throb, remembering how it had massaged his insides. Sarah touched his chin, still covered in dried cum and made him look at her, a mischievous grin on her cute face.

"Listen to me, slut. I know you can't resist my dick. If you ever want to taste it again, let alone get stuffed with it, you'll do as I say, capisce?"

Adam whimpered, torn between his undeniable desire for his sister's huge tool and, well, the fact that none of this should be happening. Why wasn't he freaking out again? Did the pills...

Sarah got fed up with her would-be cumsluts indecision and grabbed Adam's hand, yanking it into her crotch. Under his touch, Adam felt his sister's prick slowly hardening, throbbing with her heartbeat.

"Well? I'm waiting, slutboy."

Adam's eyes glazed over slightly. The throbbing, the swelling, it promised him the same pleasure he had experienced earlier. Would he even be able to live without it if he declined? A particular strong lurch made Sarah's jeans creak at the seams and Adam gasped involuntarily. His libido made his decision for him.

"Oh god, yes! I'll be a good little slut, just please, promise you'll fuck me again!"

"That's what I wanted to hear. Alright, get yourself cleaned up, slutboy. If we're gonna make the most out of Mom and Dad's vacation, we're going shopping."

Wait, going out? Like this? He probably didn't even fit into his own clothes anymore, not with that rack. His nipples crinkled and stiffened as he became _very _conscious of the weight on his chest.

"Th-the mall? But I... look at-"

"Don't worry," Sarah interrupted, "I have a plan. Just get in the shower. And don't you dare play with yourself. Remember: You're mine."

Adam was both startled and intimidated by the assertiveness of his sister. Cowed, he got up and went to go shower. His sister remained behind and let out a shuddering breath. What a rush! The power she had over her brother made her dick throb and ache, almost ripping out of the confines of her jeans. Her left hand caressed her huge bulge lightly, but she drew it back. She had to prepare a few thing before her brother was done showering. Not to mention the fact that she didn't want to blow her load without her cumslut around to lap it up.

Meanwhile, said cumslut was fighting a losing fight against his libido. The hot water streaming over his tits felt amazing, flowing down his navel and then over his sensitive mound. But his sister had forbidden it! Whining softly, he started lathering up, barely able to pull his hands from his breasts after spreading the soap liberally across them. Afterwards, he moved down over his stomach and back out to his hips... Wait, out?

Gasping, he checked his hips and ass. It wasn't much, but noticeable nonetheless: His flat ass and narrow hips were a thing of the past. All the Growth-X-contaminated pre and the creampie his sister had given his ass must have been responsible, right? Somehow, it didn't terrify him as much as losing his penis had. After all, maybe his sister would like it? If he had a bigger butt, he could pleasure her dick even better and be rewarded with her...

A knock on the door shook him from his reverie. Sarah, not waiting for his reply, entered with a duffel bag.

"What the... still not done, slutboy? C'mon, rinse off, we've got places to go, people to do!"

Snickering at her own joke, she set down the bag and feasted her eyes on the sight of her stacked brother finishing his shower, relishing how his bouncing tits jiggled as he dried himself off. She had always had a thing for both girls and guys and had even pegged her last boyfriend with a strap-on, so her brother changing as he had and herself now sporting the real thing between her legs was like a dream come true.

Adam was done and looking at her expectantly. His eyes kept straying to her strained crotch, always flitting back up. He didn't know what she had planned and was understandably nervous.

"Alright, slutboy, put this on," Sarah said, holding out a stack of clothing towards him. Adam took it and saw that it was a pair of skinny jeans similar to those Sarah was wearing, a simple white top that showed surprisingly little cleavage and the most frilly panties he had ever seen. Wide-eyed, he looked at his sister. She jerked her chin at him, indicating the clothes in his hands. Adam gulped and held the panties in front of him. With a deep breath, he stepped into them, pulled them up and was amazed at how snug they were around his ass and crotch. The jeans were a bit too wide, still, but maybe Sarah could... Adam shook his head and put on the top. It was obvious that his sister was less gifted in the chest department - due to the size of his breasts, he could not pull it down all the way and his midriff was bare. Not to mention the way his nipples were visible through the fabric. He caught sight of himself in the bathroom mirror and was surprised how hot he looked. Well, from the neck down at least. While his face was not the epitome of manliness but instead an the male side of androgynous, his hair was undeniably cut like a guys.

"Y-you really want me to go out like this? I look weird."

"Not for long. Sit down and let me work my magic," Sarah answered and pushed him down on the toilet.

Taking out her make-up kit, she got to work.