The gender-changing device was like some weird cylindrical puzzle. Holding it vertical, on one side was a male body, and the other had a female body. Sticking out from the cylinder were depictions of sexual characteristics, made to slide to various locations on each body, including transferring to the opposite gender. On top of the device was a dial and four buttons. The dial was currently pointing between the male and female depictions. The buttons were in pairs, each pointing to one or the other gender. The buttons pointing to the female side were pressed in, and the buttons pointing to the male side were depressed.
Alex slid the penis up the male body. The next stop up was the navel. It settled in with a click. Almost immediately, Alex felt his body change. Lifting up his shirt, he saw his penis sticking out where his navel used to be. Excitedly, he pulled off his clothes, and examined his body. He held his penis in his hand. It felt just like his penis, but with the strange sensation of feeling it in a different location. Looking down at his crotch, his balls were still in their usual location. Their location was determined by an attachment separate from the penis. Feeling where his penis used to be, he expected to find smoothness, but instead found a small slit. His urethra. There didn't seem to be an attachment for that. In fact, he noticed that it was part of the main piece, unmovable.
Interestingly, though, facial hair was movable. He started sliding that away from the male body, towards the female body. Surprisingly, it first settled in the middle. Alex felt a light tingling on his face. Rubbing it, he found his face smooth. Even better than when he shaved it. The only hair left on his face was his eyebrows. Liking this change, he left the facial hair attachment where it was. (Though it was tempting to move it all the way to females.)
Alex turned his attention to the buttons on top of of the device. The two buttons pointing to the male side each had an image on it: a pair of circles, and what looked like a limp penis. Same with the two buttons pointing to the female side. He pressed the male button with the circles on it, and it clicked in. Suddenly, he felt a sucking sensation in his crotch. Quickly reaching down, he found his crotch was now almost perfectly smooth, leaving his urethra as the only feature. He didn't lose his balls, though. He could still feel them, deep within his body. Which means...
Alex pressed the other button on the male side, and immediately felt his penis get sucked back into his navel. Investigating it, though, it looked tighter than it did as a navel, and the area around it looked puffy. Rubbing it, he found it as sensitive as the head of his penis. He stuck his finger in. It felt like he was fingering a sexual organ. Now, not only did males have their penis on their bellies, but it was an internal organ, as well as their testicles.
Pulling his finger out, he quickly depressed the buttons on the female side of the device. He wouldn't be able to look until later, but he assumed he just made female sex organs external.
That left the dial on top of the device. Throwing caution to the wind, he turned it all the way to the male side, expecting something to happen to him. But, looking himself over, nothing seemed to be different. So, he turned it all the way to the male side, and he felt ripples across his body as his whole self changed! He looked down, and the first thing that greeted his sight was a pair of breasts, large enough to cup in his hands. Reaching down to his belly, he found his navel back to normal. But his biggest surprise was what he found hanging from his crotch.
It... resembled a male penis? But rather than a small slit at the end, the opening was more round, and curved inward, like something was intended to go into it. But it was so small, he couldn't imagine what that would be.
And of course, hanging behind his penis was a ballsack, though if he had to guess, it contained ovaries instead of testicles. He found no sign of a urethra, though. Meaning, he likely would pee from his female penis, much like he used to with his male one.
Alex was certain that the slider changed him into a female. But he wasn't sure what that meant. But if this device changes the entire world, an easy solution is to look online and see what he could find.
Looking up pictures of people, he initially didn't notice anything out of the ordinary. But as he continued looking, he realized that there were no men. Doing a search for "male", all he could find was the mentioning of animals. Did all men somehow get turned into animals? No, doing a search for "female" did the same. Apparently, gender terms now only applied to animals, whereas human beings were only one gender: "human".
Furthur research showed that the organ was still referred to as a "vagina", though. In fact, while it resembles the male penis of animals, and can even become erect, sexual activites cause the vagina to... pump inward, as though it were trying to suck in male sperm. But with no male humans in existance, scientists hypothesize that the sucking motion is an evolutionary leftover from when humanity had two genders, though no evidence has been found to prove that humanity ever did.
That said, unlike animals, humans have no need for sexual partners, though some do for recreation. Instead, humans reproduce asexually. This occurs as a survival instinct. When human interaction is limited (resulting in the detection of fewer pheromones), they will produce a child to ensure the continuation of the species. Because of this, child birth tends to be more common in less populated areas. Though humans who are less social can also find themselves pregnant, even if they live in a big city.
Alex couldn't believe everything he was reading. There was no doubt about it -- the dial on top of the device affected the ratio of men to women, and he just created an all-female world. One with self-reproducing, external sex organs!