What has come before:
It was Jon's last year in high school, just after spring break, and he inherited a magic rock, which he used to make a cloning machine. And to wish that nobody would find it particularly strange that he had a cloning machine or what he did with it. The machine let him combine and change attributes, and he used it to bring his fantasy to life: to make a female clone of himself, Jonnie. Exactly the same as him except that she's a girl, she's attracted to him, and she isn't upset at being a girl. An extra wish let him make it so that the clone could never become a guy, either.
The plan defied years of bad science fiction stories by working. Jon's girlfriend was his clone, who remained identical to him in all respects except the bare minimum of difference. They agreed not to consider each other brother and sister, and to treat their shared past. and the stone, as belonging to both of them. Any wish that one of them hears is treated as though both of them heard it.
Jon let other people use the machine, and at one point Sarah used it to clone herself a younger sister (by 4 years), who is either also called Sarah or is called by her new middle name Leah. His friend Joseph also wanted to use it to create a submissive catgirl clone, which Jon refused, but found himself accidentally making happen anyway.
Jon and Jonnie had to do without the stone for a week in order to teleport it around the world so that all records would be correct. During this time, Sarah and her clone, smarter than they appeared, investigated and managed to gain at-will wishing powers that Jon and Karyn don't know about. Also during this time, Jon had to deal with Joseph's clone not liking her situation, which he handled by warning Joseph that the submissiveness could wear off.
It also turned out that Jon got his clone pregnant, which they handled by wishing that the baby would disappear until it was almost time to be born.
Over the rest of the year and during the summer, Jon and Jonnie used the stone to carry out fantasies, to make Jonnie like wearing a dress to the prom, and to temporarily both become girls, when they dated a guy (once) and almost dated a lesbian ex-girlfriend Katie. After the summer came college. Sarah went to a different school, Jon had a roommate named Paul, and Jonnie was roommates with Karyn. Which brings us to the present....
