As Jeff waited, he quickly regained his sense of sound and all of that, only to be greeted by his sister's voice. "Jeff! Where'd you go?? Jeff!!" He wasn't sure what to think about this. She remembered him, and it sounded like her voice was right above him...
With a moment of thinking, while still hearing Maria's voice, he put two and two together and realized what happened. "Wait... oh shit.. I'm in my sister right now..."
He could hear everything, and feel slight movements as she was looking for where he went. "Jeff.. what happened... where did you go..." She grew more worried, trying to find him. He listened in for a few hours of her looking everywhere in the house, before finally their mom came home. She ran down quickly; "Mommy!"
He couldn't hear what their mother was saying, but he could hear Maria's voice pretty effectively. "Mommy! Jeff's gone missing!" He could barely make out "Jeff? Is this some new friend you made?", showing that she was properly effected. But why wasn't Maria..
There was a conversation between them, as Maria was confused on how her mom suddenly forgot Jeff existed. She started with the assumption that this was somehow a prank, but after a week, everyone she found seemed to forget Jeff even existed, including some of her friends that she didn't have mutual friends with.
Around this point was when morning sickness began kicking in. Her younger age caused her belly to be a bit more noticeable, and since she was still only a kid, she didn't cover her body as much as older girls. This made it a bit more noticeable, and after the one-month mark, their mother decided to get it checked out.
As the doctor noted, Maria's case was extremely abnormal, as she still had her virginity and hadn't even gone through puberty, despite having a very recognizable pregnancy that was approaching two and a half months.
The pregnancy continued on, and wasn't aborted despite the bizarre circumstances. Jeff's genitals were making their distinction noticeable, and as if it wasn't enough to be inside of his little sister, he noticed he didn't even have a penis anymore. It had been entirely replaced with his new baby vagina.
Maria seemed to stop thinking about Jeff in his previous state, only sometimes doing so when she seems to be alone. One of the few upsides of this is that he'd now been made aware of some more friends she had, which she'd never told him about. But he wasn't sure if it was worth it, having to spend eight months in a small crevasse his little sister contained within her.
When the pregnancy came closer to it's end, it became harder and harder for Maria to wear regular clothes, as her belly was reaching the floor. She ended up wearing unzipped onesies most of the time, as it was the best she could get without being naked. There was an increase in bullying as well, but she tried to ignore it to the best of her abilities.
Inside, it was pretty tight for Jeff. He was able to move around a bit, but he could sometimes feel the lower areas dragging across the ground. There wasn't even enough room to look at the Chronivac, and when Maria's water broke and it came time for his rebirth, the only option he could initially think of was trying to shove the Chronivac up into his privates and fish it out later.
With the chronivac inside his own vagina, he squeezed through the small virgin tunnel and was reborn into a new life. The tight squeeze left a bit of blood from his sister, as the doctors did their thing. With the verification of Jeff now being a girl, she was given the name Jenny, with Maria intending it to be similar to Jeff as a small reminder of her lost brother.