Swap both of their genitals

He was always curious about this. The older he got, the strongest got his curiosity for the female anatomy. As a kid, he was fascinated by girls not having penises, thinking they lost it somehow. He had to chuckle as he remembered that.

Zack knew from long ago that if he ever got powers like these, he would try them first by taking a girl's genitals. His curiosity about it got more and more over the years, and sometimes he felt really disappointed at the thought of never being able to feel what it's like to have a vagina. However... this was about to change. Hopefully.

He didn't want anything to go wrong. He went over the 'REALITY ALTERATION' switch on the device, checking how easily it was to switch from 'on' to 'off'. He really didn't want his sister to notice her reproductive system missing, being replaced with a dick and a pair of balls, at least for now... the switch was surprisingly hard to flip.

According to the manual, he should simply hold down his thumb on the sensor atop of the device, think about the swap he wants to make, and then press the button on the underside of it. Quite convenient, he thought, especially compared to what he always would have imagined such a device to be.

One last time he chuckled to himself at how ridiculous this whole situation is. But he was determined to try.

His sister was lying down on her back, her crotch being visible through her tight cotton shorts - usually what she chose to wear at home. He checked once again whether the reality alteration switch was on 'ON', closed his eyes, and then concentrated on him having his sister's genitals, and her having his. It was surprisingly easily, although something like that was mentioned in the manual, easier concentration to avoid false swapping.

He pressed the button. He felt his whole abdomen and penis tingling, until it was over in just a second. He ripped his eyes open, and saw a very noticeable bulge in his sister's shorts. It had worked.

Zack felt a massive change in his abdomen and crotch region. He FELT it had worked. He was beyond shocked, but on the outside still seemed surprisingly calm. If he still had his dick, it would be rock hard by now.

He rushed into his room, and locked the door. Instead of getting hard, he felt a slight throbbing in his crotch and a spot of wetness in his... boxers? They seemed to have changed to fit him better...

Zack didn't waste any more time and ripped down his pants and boxers. He found them to be slightly shorter and more fitting for the flat crotch he had now - he had to control himself to not immedeatly start masturbating furiously with his sister's equipment.

The pants and altered boxers were tossed aside, and Zack went infront of his mirror to admire his new genitalia. Between his inner tights was a trimmed, young slit, massively out of place between the hairy legs of his. A small line of pussy juice was rolling down his inner tight.

He used his hand to part his new pussy lips. Inside, he was greeted with pink folds. He was extremely aroused by this whole situation. Having a cunt itself was enough to make him go crazy.

Zack couldn't take it anymore. He dropped on his bed and started massaging his pussy, moving on to his clitoris. Just touching it a bit was enough for his legs to shiver and his toes to curl. The new sensations were overwhelming. He knew that women had it better when it came to pleasure, but this was straight up unfair. And unreal.

After teasing his own clitoris for a bit, he already felt close to cumming. However, he wanted the full way. He inserted his middle finger into his sister's snatch, and started to penetrate it slowly. Once again, his whole nerves and senses were overwhelmed. The pleasure he felt and the sensation of having his finger inside him was absolutely alien. And he loved it.

He got faster and faster and it didn't take him long to orgasm, his whole body shaking, and even moaning slightly. He muffled himself and felt pure ecstasy from him crotch all over his body.

"I want to keep it...", he thought. The sensations were absolutely worth it, he knew he could do it with reality alteration. He pondered his next step after getting over the afterglow of his first female orgasm his sister's vagina gave him.