You just swapped your manhood with the vagina of you sister! You're standing in front of the mirror in your room, looking at the flat, feminine spot on your reflection - your new crotch. You didn't even noticed Alexis, who was entering your room. She let you awake from the shock by touching you.
"Phillip, what did just happen??"
"Ah! Alexis, I-I-I'm s-sorry!!"
"So you did this?"
You were silent for a moment, but answered then.
"Yeah... well... how should I explain... I was just relaxing in my room when a strange voice spoke to me, in my mind, telling me that I'm able to swap physical body parts of other people with mine by wearing their clothing... and I wondered if it worked..."
"Why didn't you tell me this earlier? I would have borrowed you something. And why did you exactly put my panties on first?"
You were blushing, red of embarrassment.
"I-I-I just wondered how this would feel like..."
"Well... actually, I always wondered what it would feel like to have penis... after noticing the bulge in my pants, I thought that I was dreaming... anyways, I guess you want to try out my vagina, don't you?"
You were even more embarrassed.
"Y-Y-Yes..."
"Hey, that's great! So I'll take care of your manhood. You can use my vagina like you want, as long as you don't damage her."
"Uh... s-so you're not upset? I thought you would freak out..."
"Well, I can keep a cool mind, and you know me, I'm not like that. So, for how long should we keep our genitals swapped? I suggest an open end.", Alexis said with a smile.
"E-E-Err... okay, I guess...", you answered, stuttering, reaching a hand down to your new crotch, feeling the vagina trough your sister's panties. You noticed that the bottom of the panties were soaked with vaginal juices you produced, because having a girl's reproductive system turned you on. Alexis had also red cheeks, she was embarrassed too, but still kept a cool mind, just like she said.
"Don't be so shy Phillip, after all, we've seen each other 100 times naked, we're bother and sister. But okay then, I'm in my room checking out this new awesome thing I got. If you have any questions for the Girl Experience, feel free to ask", she said in a happy tone before leaving to explore her new penis."
You calm down and decided what to do now...