Jeff had an idea, and decided to go for it. "This could either be fun, or backfire horribly." He minimized the Chronivac window, promtly leaving his room as he headed to where he knew his youngest sister, May, would be.
Entering the room, having avoided his other sister, he walked over to where she was playing. He picked her up, and set her somewhere more hidden from sight. He reached down and pulled her skirt up, before pulling her full diaper down, his sister looking cute and confused. He was about to enter, before deciding to do something else. "It may be a bit tight right now, and It'll be where I'm located soon anyways..."
He moved his hand over to her urethra, sticking a finger in; He could barely fit it in at all, and it was extremely sticky. He moved his finger, trying to open it up slightly as she twitched in pain.
He put her onto the ground, sitting in front of her as he kept her on her back. He took in the view for a second, before the stench of her diaper got him; "I'll have to deal with that first, it's too much!"
Trying to go fast, he pulled her diaper all the way off, disposing of it and clearing the stink; He didn't grab an extra, as he didn't know how to put one on, however. He laid her down on her back, and positioned his feet near her pee hole. "Alright, it's time..."
He pulled her forward, his feet going inside her small urethra. He could tell she was in a lot of pain, but he continued on, pulling himself further into her tiny hole. After a bit of pulling, the Chronivac kicked in, regressing him down and shrinking him as he entered position; He entered a bit further, having his penis stick out a bit.
After adjusting his position slightly, he could only chuckle at the thought of this look; Him at a young age laying on his chest, and right behind his small penis is the urethra of his younger sister, as he was between her legs. May's labia was soft, comforting his crotch and encasing his penis almost entirely as it teased her vaginal opening slightly.
Pushing himself up, he got his position to where - Aside from his lack of legs - it appeared as if he was sitting between her legs. At that point, he waited a bit...