He thought about it, but then realized he had the perfect target waiting. "This will go great.... I think." He heard his sister talk about wanting to know what it's like to be a boy in the past, but couldn't quite tell if it was in a joking manner or not.
He went out of his room to find where his sister went. "She can't have gotten far." He checked the kitchen and living rooms, before heading down the hall to her room. "If she's not getting a snack, she's probably in here."
He walked into Alice's room, and didn't see her. "Huh, she's not here?" He went to leave, but noticed her bathroom door slightly open. "Unless..."
He went over and opened the bathroom door, looking around. Alice was near the back of the room, facing away from the door; She was in the process of taking her clothes off to take a shower. Jeff took this chance, and closed in.
He quickly closed in on his sister as she took off the last of her clothes, choosing not to focus on her underwear. He couldn't help but feel aroused; He hasn't properly seen a girl naked, outside of changing Alice's diapers when she was a baby. Alice stepped into the shower, and Jeff slipped in behind her.
Jeff managed to sneak around Alice getting in. Alice closed the door behind her, and when turning back around, that's when she saw him. "Jeff? What are you doing here?" Jeff remained quiet, and lifted his ten-year-old sister into the air.
She stared at him, but wasn't sure what he was doing. He sat down on the floor, and set her down in front of him, spreading her labia to reveal her vaginal and urethral openings. He moved around her, forcing her onto her stomach before aligning his toes with her urethral entrance. "What are you doing?"
He grabbed her legs, and pulled them back. Alice screamed in pain as his body was forced up her pee hole, but he kept going. He got up to his waist inside before the Chronivac kicked in, regressing him down to her age before shrinking him to half his usual size and pulling him in a bit further. The Chronivac attached his legs to the sides of her urethra, so that he doesn't slip out accidentally or get pulled out. This connection then caused Jeff to feel the lingering pain Alice felt from shoving himself inside her.
Once Jeff was in, Alice was breathing heavily, calming down from the pain. She was still laying on her stomach, with Jeff on the other side laying on his back. She managed to calm down, and sat up, her labia perfectly hiding Jeff inside despite him being far bigger than it. She looked around trying to find him. "Jeff? Where did you go?"
Jeff pushed himself out of her labia, causing him to hang down past her knees. He raised his body up as Alice looked down, and they met eye contact, Jeff's current state causing him to barely get up to her undeveloped chest. Alice was still confused, and the two stared in silence with the exception of Alice's breathing.
Breaking eye contact, Jeff leaned back down, managing to fit himself back into her labia. Alice stayed speechless for a moment, before returning to the shower she started. Jeff couldn't tell if she was trying not to think about the situation, or what.