A few days latter, while Jenny was at a friend's house and her parents still at work, her little sister, a little pest named Julie, decided to take advantage of being alone at home to explore Jenny's room.
As the pest she is, Julie noticed the Chronivac and decided to study it. She rapidly discovered it was a machine capable of rewriting reality and, if she believed the thing's historic, her big sis used it to merge herself and her boyfriend into a two minded human looking monster, with Jeff clearly getting the short end of the stick, which made Julie very uncomfortable for some reason.
Maybe she should do something for poor Jeff, even if she didn't have any memories of him left. After all, while the guy liked his situation, it was only because the Chronivac made him. And if she played her cards right, she might even get something for herself out of it.
So she made it so Jeff used to be a childhood friend of Jenny before becoming her boyfriend, (a change in their relationship they hid from Jenny's parents) and was visiting when their uncle on their mother's side reappeared and became part of their lives, that Jeff was at Jenny's side when she surprised that monster trying to rape Julie, to rape his own niece, both of them doing everything in their power to stop the man.
That was without counting on ‘uncle Freddy’ who always had a knife on him and used it to stab Jenny and Jeff. Normally, the wounds inflicted should have killed the two teens, but instead activated something in Jeff and he turned into some sort of parasite, letting his human body behind and, guided purely by new instincts, entered Jenny's body through her wound, closing it behind him.
Once inside Jenny's body, still guided purely by instincts, he started changing Jenny's body so the result of their ‘fusion’ stayed the same. So her vagina would double as his mouth, somehow able to speak in his old voice, and this without causing any orgasm to Jenny. Instead of teeth, that ‘mouth’ gained 3 row of retractable hook, so nothing entering it could go out if Jeff didn't want it to, and a tongue that had specially evolved so it could coil around a penis and masturbate it, making it more akin to a tentacle, which was also doubling as his penis. By this point Jeff had recovered enough to go against his instincts and not turn Jenny's body into his own.
But while Jenny still look like herself, and usually have control of her body, Jeff could at any moment override it taking control of their movements. (In practice he only do it after asking permission when he really want to do something, or if Jenny ask him to.)
The presence (and ‘death’) of Jeff made the fight slightly more loud, but it was enough to make the rest of the family come into Julie's room, only to see a blood covered and now stronger Jenny break her uncle's arms while trying to separate him from her traumatized sister before she could be raped. (Jeff turning into a parasite before fusing with Jenny's body and modifying took only a second.)
Julie had made sure that Jenny and Jeff would know she was the one who changed the reality, but wouldn't herself remember the old one. From her point of view, she never was victim of an incestual rape, even if it was a near thing. And unlike in the old reality, were nobody in the family believed her sister when she denounced their uncle, this time Freddy would go to jail for his action, which included murdering Jeff and trying to do the same with Jenny. Instead of acting even more like a brat toward her sister after the incident, Julie would now seek her for comfort.
Like before she altered their change, Jenny's doctor and a special monster wing at the hospital helped her and Jeff cover their new circumstances, hence why Jeff was legally dead, with very few persons knowing the truth.
Julie got out of her sister's room, thinking she was simply searching for one of her textbooks, thinking she might have left it the last time she had asked Jenny (and Jeff) for help with her homework.