He decided to click the Bodysuit option; Some more options opened up with this menu, allowing him to decide on how she'd be worn or the amount of control she'd have. Having not previously thought about this, he took a bit longer to decide.
He decided to set it so that she can be put on from any area, and set the second option to where whoever wears her has control, but if the wearer isn't actively taking control she can move on her own. To avoid any issues, he also put in that the wearer will be adjusted to an age where they would fit inside of her comfortably. Satisfied, Jeff clicked confirm, and the Chronivac started it's work.
Jeff watched the progress as it did it's thing, strangely excited at the thought of wearing his younger sister. Only a few minutes later, the device finished up, and Jeff went out to find Alice.
==========
Jeff ended up locating his sister in her room, about to sit down for a game. He snuck up as she was getting comfortable, catching her by surprise as he picked her up out of her chair. It took her a second as he carried her back to her bed, before she started to struggle in his grip. "Let me go!"
He pinned her down on her bed, with her struggling as he held her down. "What are you doing, let me go!" Ignoring her plea, he reached under her skirt and pulled whatever she was wearing underneath down, not caring to look. He leaned down, attempting to dodge her kicking as he moved his face closer to her genital region. "Jeff, stop!"
He was able to smell it now, and he decided to get it through. Rushing his face forward, he closed his eyes, feeling as the modifications from the Chronivac let him slide on in. He felt her struggling stop as he entered, pushing further in. With his position, he could hear her breathing quickened as he slid further into her vagina, going as deep as he could go.
He hit a wall, and the Chronivac did it's thing. The rest of his body was pulled in as he was aged down, the feeling of his sister's vaginal walls fading as his legs fully entered. He tried to open his eyes, but everything was black. He heard her breathing again, slowing down as he could see through her eyes.
As everything settled in, he sat back and watched as Alice seemed confused. "What... what did he... was that even... wha..." She leaned down, looking for where Jeff went. "Where did he... what..."
She pulled her skirt up a bit, still slightly hiding her genital region, not seeing Jeff anywhere.