Wholesome family bonding!

Monica led Steve into his room and closed the door behind them.

Steve glanced around at his room, which was, to no surprise, messy. He remembered making his queen-sized bed up before leaving for work, but now its black and gray coverings were strewn all about with his sister's pink laptop laying in the center, and there was no way that the snack wrappers and soda cans scattered around the floor and surfaces belonged to him. There was no telling how long Monica had been hanging out in there that day.

Regardless, there were more pressing things to be concerned about.

For some reason, Monica was now skinny, busty, and bottom-heavy, as if by magic. Even though Steve couldn't form together more than just a few words before his very limited attention span went back to thinking about how full his balls felt, he knew that something weird was going on. As he briefly wondered what was happening, Monica walked him over to his bed and sat him down on the edge.

"So, I've got something really cool to show you." The plucky young blonde giggled, plopping her round rump right beside him on the edge of his memory-foam bed, her big bubbly thigh mushing up against his own toned leg. "But you have to promise me that you won't freak out."

Steve took a long look at his sister's excited smile and expression, his heart skipping a beat at the sight of her big blue gaze looking up into his slack-jawed face.

He couldn't remember the last time he'd seen that kind of look. His sister had always been chubby, but when her cat died shortly after Monica turned 19, she sunk into a deep depression and really started to gain weight. Since then, she stopped smiling like was doing right then, and magically stupefied or not, Steve was speechless.

"Promise." She said, a little more demanding this time as she held up a fist with only her pinky-finger extended. "If you do, I'll make you smart again."

Steve chuckled, blushed, and rolled his eyes as he raised his hand and accepted her pinky swear by locking one of his around hers.

"Awesome!" She cheered, then leaned back to grab her laptop before placing it on her lap. "This thing is so cool, I've got a feeling that you'll lose your shit when you see this!"

Unfortunately, Steve had no idea what he was looking at when the computer unfolded and the screen lit up.

Half of the screen was showing him, sitting in the exact position he was sitting in and still wearing his dress-shirt and basketball shorts, which were still pulled down to the middle of his thighs while his exposed and average-sized erection throbbed angrily from his shaved crotch.

His eyes followed the cursor as it moved to the right half of the screen, which listed a multitude of words that had slider bars under them.

The cursor stopped over one, but Monica's finger on the touch-pad mouse hesitated, and she looked up into Steve's confused and handsome face with a nervous smile for a brief moment. She turned back to the PC and switched the tabs at the top of that half of the screen, and the words underneath seemed to change, but Steve still couldn't make out what they were saying. The cursor quickly found a new slider as Monica's busty chest rose with her heavy breathing.

"Y'know, we can hold off on making you smart again for a bit." She whispered, her breath shaky. "I feel like it would be a wasted opportunity if I didn't have some fun with my big sexy brother while he's a horny idiot."

Steve tilted his head to the side, mildly offended by her completely accurate assessment of his current state.

Then, whatever he was thinking quickly vanished as he felt his hard cock come alive with all different sorts of bizarre and pleasurable sensations. His eyes went wide as he leaned back some, watching as his throbbing erection began to grow and extend. In the span of just a few seconds, and moaning all-the-while, Steve's cock had grown from a modest five-inches in length to twice that, and his shaft had to be as thick as Monica's forearm now.

"Whoa..." Steve dumbly mumbled, reluctantly reaching forward to wrap his hand around the base of his huge steely cock. "It's, like..."

"Fuckin' huge..." Monica said, drooling at the sight of her brother's gut-shovel. "And your balls..." She cooed, pressing up against the side of his body as one of her hands slithered across his thigh and snaked around to gently cup his silky-smooth jewels, which resembled that of a tennis-ball with a slight fleshy crease down the center. The contact **** a moan to escape from her older brother's lips, who was even more light-headed now. "Jesus Christ, Steve... I feel like I could get pregnant from just looking at this."

Steve squeezed his shaft as tight as he could, barely registering Monica's words as his heavy heartbeat drowned out any other sounds. He pulled up on the length, then slowly tugged it down, letting his foreskin unwrap most of his leaky cockhead. He turned to look at his sister and her new curves with lust, half-tempted to rip off her fairly conservative PJs and go to town on her petite figure right then and there.

Monica pulled her hand away from his sack as she turned to meet his gaze, and her smile fell ever-so-slightly upon seeing his expression, the look in her eyes instantly becoming anything but platonic and sisterly.

She quickly turned back to the laptop and typed a lengthy string of words into a black bar towards the bottom of the screen, smacked the enter key, and then closed the laptop before sliding it under the bed.

One of her hands forcefully slammed against Steve's broad and sturdy chest, pushing him down onto his back on the bed.

The squirrely twenty-five-year-old then mounted her brother, who just had the wind knocked out of him, straddling his chest as she pulled off her top and tossed it to the side in one fluid motion. This allowed Steve to see her new and beautiful torso without any visual barrier. Her big, sagless, tear-drop-shaped tits jiggled and sloshed around with any and every movement she made, and the plush warmth of her toned thighs straddling his crotch while her sizable cheeks acted as very plush buns to hotdog his rock-solid fuckstick through the fabric of her soft PJ bottoms.

Acting purely on instinct, Steve's hands grabbed at her hips as she began to grind her moist crotch against his lower-abdomen. The fact that Monica was his sister was lost to him completely, and some sort of primal urge to breed with the blonde bombshell on top of him took over completely. Steve's hands roamed up the sides of her body, taking in the smoothness of her flawless skin before he palmed Monica's big tits.

He began to gently knead them, and coupled with the whimpers and moans he was eliciting from his sister's mouth, the man with a freezing-temperature IQ was going insane from how amazing every inch of her body felt against him.

In a flash, Steve's hands were on her waist and he was spinning them around, reversing their positions as he threw her down onto her back on the bed next to where he was. Standing over her and looking down at the sweaty, shivering, and grinning slut on his bed, he returned her lustful smile before reaching for the crotch of her bottoms and ripping them open with a few tugs to reveal her tight glistening pussy. Steve's shorts finally slid down to his ankles as he wasted no time in grabbing the base of his giant dick and lining it up with the entrance to her cunt, and Monica gasped and grabbed her big jiggling tits in preparation, trying to prop herself up and look down between her valley of cleavage to witness the extremely taboo penetration.

Nothing in Steve's mind told him that his cock wasn't going to easily fit inside of her, not that it mattered.

When his hips first thrust into her, the head of his cock entered her pussy with ease, but the sheer tightness of silky wet flesh around his meat caused him to groan along with Monica's high-pitched squeals. In just two more mind-bending thrusts, Steve completely bottomed-out in his sister, the visible outline of his throbbing cock bulging out along the length of Monica's abdomen. Monica's eyes rolled back in their sockets as Steve began to fuck her with all of his strength and the skill of an experienced porn star, and it wasn't too long before he could feel his first orgasm building up, all while his sister seemed to be in a constant state of euphoria.

This was only the first orgasm of many for Steve, and the adult pair of siblings spent the rest of the night fucking what was left of each other's brains out until they passed out from sheer exhaustion.