Jon was still smiling...yet incredibly nervous at what his sister's reaction had been to suddenly ;losing' her breasts. Luckily for him Zoe had passed it off as an incredibly vivid trick of her imagination. Jon waited around until Zoe had finished her shower, and then he got ready when he heard the bathroom door being unlocked and then opened. Stepping partly into view, he pointed his index finger at his unsuspecting sister.
"Give me that vagina!" Jon exclaimed quietly, so Zoe didn't hear him. He was watching his sister walking back to her room, wrapped in a towel, her hair damp but not dripping wet. A tingling sensation suddenly hit his crotch and Jon looked down in trepidation. But his slight fear turned to excitement when he felt his penis 'withering' away. At first it was just like a hard-on gradually dissipating, but then he felt his entire groinal area inverting. His pelvis cracked a little and reshaped as he felt his penis get sucked up into his body, followed by his testicles. In a few second...his 'junk' had morphed into his sister's vagina.
"Wow!" he gasped, as he began rubbing in between his legs. Then a quick glance at Zoe before she disappeared into her room showed a distinct 'bulge' in the front of the towel that was wrapped tightly around her.
Once Zoe had closed her bedroom door, Jon disappeared back into his own room, having successfully switched genitals with his younger sister.
After a brief moment's hesitation, Jon then pushed his shorts down around his knees, followed by his boxers, and he got a first glimpse at his new sex. A perfect pair of pink, vaginal lips with a thin strip of dark pubic hair above. Jon was glad to see Zoe kept hers trimmed.
