Stew enjoyed his work tinkering and designing new tech. He'd then go ahead and sell his patents for money. He was decent enough at his work that he would have enough money to live off of, and was continuing his work out of curiosity and desire. He so happened to be working then noticed on his worktable a strange device that had randomly appeared. Stew out of curiosity looked at the sex machine's case and saw one button, a setting for fertility, and a setting for permanence... He wasn't comfortable enough with the unknown device being on a permanent setting when he didn't know what it did, and he neither wanted it to accidentally make him infertile so he set it to fertile.
Now out of curiosity Stew figured out how the case was put together, and managed to take the case off safely and was mesmerized with what was inside. His first thoughts were this tech was obviously not of this world. His second thoughts were "Oh... so that probably works kind of like that and... is this on?.... Oh is this thing the battery?"
Awhile later a story above him was his girlfriend Stella who was getting annoyed. Stew told her that he'd be ready an hour ago. Her food she had made was cold, and she was no longer in the mood for snuggling or any real kind of intimacy. He was always like this... tinkering so much and practically ignoring her. She knew Stew didn't like her down in his lab, but this was it she was going to down into his lab, yell at him, and then storm out and quickly check into a hotel as she'd suck it up and ask to see if she could go back to her parent's house while she figured out a housing situation.
As the angry girlfriend stormed down the stairs Stew figured that he was done for the night trying to figure out how the remote worked... Or at least until he figured out what it actually did. The case was back on completely and now time to see what happened when he pressed the button... nothing seemed to happen or light up. Since there was a fertility section what if it worked on living things? He pointed to himself and... a light lit up! What the heck did that do? *Thump Thump Thump* went Stew's angry girlfriend's steps as she came down the staircase. Stew was annoyed that she was coming down, but he supposed that he was rather late... As Stella was visible she said "Stew! It's been over and hour and I've HAD I-" Stew pressed the button again as the sex machine was pointed towards Stella, and then Stella seemed to grow large and muscular. Then the next couple of moments were a bit of a blur, but Stew heard the grunts of an unfamiliar man and some girl moaning as Stew felt incredible feelings as he felt a warm liquid feel his insides. In the haze of sex as he felt himself resting on a warm, firm chest he looked down at himself and saw a relatively small pair of boobs on his chest which kept shrinking until he noticed the firm chest his head was resting upon felt a lot more squishy.
Stella pushed Stew off her breasts and asked "What Did YOU INVENT?!?"
Stew looked at the Sex machine and said "Well... It just kind of appeared awhile ago, and I was examining it for awhile... I think this thing swapped our genders and made us make love."
Stella nodded and stated "So... We are in some porn plot?"
"Maybe... but you know that experience gave me an interesting idea!" but what was that idea?