Jenny thought for a moment before stating her answer. "Hmm, I think I want to be your sister. Your ideal older sister."
"My ideal older sister, are you serious?" Jeff reacted. "Why would you want that?"
"It seems fun. If I was your older sister, I would get to live together. I get a break from my parents, and we get to hang out more. Plus, you like older girls, don't you?"
"O.. of course, Jenny, but wouldn't it be weird for us to be siblings when we're dating? Like, it would be incest, wouldn't it?"
Jenny smiled. "It would only be incest if we actually do something sexual. Like we can just hang out together like a brother and sister would that you ever dreamt of. I can be supportive, I can be kind and sweet, or I can even be your beloved sister who loved you everyday. And we can make out without your... our parents around. So, what do you think?"
"Hmm... I guess we could try. It's not like it's something permanent."
After that, Jeff typed in as they opened Jenny's profile. They found a relationship tab, and there they could change Jenny's relationship with Jeff to 'siblings'. A few options appeared. The first one was who would join which family. They selected Jenny to join Jeff's family. The next option was about age. They were 5 months apart in age, not something feasible if they were to share the same mother. They could change one of their ages to make it congruent.
"Okay, now I do need to edit the age, how old do you want to be, Jenny?" Jeff asked.
"Hmm, let's see," Jenny replied. "Since I want to be your older sister. Hmmm. How about 20? A college girl?"
"Sure. I guess." Jeff edited Jenny's new age to be from 15 to 20. "Anything else?"
"Yeah. I saw something. Mental changes? Can we try that?"
"That sounds a little scary, but we can see what it's about." Jeff selected the mental changes tab. There, they could see various info and options.
"Let's try it!" Jenny said. "It's probably going to make it feel much more real. How about sliding our mental changes to 30%?"
"I don't know." Jeff was cautious.
"Okay then. 25%? 20%?"
"I guess 20% seems safe," Jeff gave in. He adjusted both of their mental settings. "Are we ready?"
"Yeah. I think so. Go ahead. Apply the stuff."
Jeff did.
He then looked towards Jenny. She was changing before his eyes. The most immediately noticeable change was Jenny's hair losing its red color, turning into a brown shade not unlike his own. Her facial features were different, less rounded and more mature. She was starting to resemble his mom, more like a younger version of his mom.
To Jeff's surprise, she grew taller, actually. It made sense with Jenny being a short 5'1", and Jeff's family being decently tall, but it was a bit counterintuitive with her getting older.
Jenny's physique changed, but the differences weren't too overt. Her frame seemed a bit wider, and her chest seemed larger and bigger into E-cup.
The changes seemed to have stopped.
"What do you think, little bro? Do I look hot as your sister?" Jenny asked in her new voice.
"Well, I'm speechless," Jeff felt a tinge of embarrassment. Jenny did kind of feel like his sister now, and it felt awkward considering that. He guessed the mental changes were in effect.
"Ooh!" Jenny exclaimed. "I can remember stuff about my new life." She seemed to be concentrating for a few moments. "But it's not that clear."
Jeff also tried recollecting his new memories. Looking at Jenny, he could remember some events, or daily affairs, how he and Jenny left together in the mornings, or how she often came into his room, bugging him, wanting to hang out and play, though that happened less after she became a young adult. Though all these memories felt distant and sparse, and only barely like his own, which made sense considering they'd selected only 20% mental change.