Yuriko knew that her sister was probably bluffing but she decided to play it safe anyway. She took off her pajama bottoms and slipped into the underwear. They were made of cotton and they felt rather comfortable despite being a little roomy in the front."
Saya grinned and Yuriko waited until the inevitable snap came and the final piece of the transformation began.
Yuriko winced as the awkward feeling of a gender change was felt around her crotch. Finally, a cock sprouted from between her legs and she gasped as it filled out the pair of men's underwear that she (or rather he) was wearing.
Yuriko pulled her waistband forward to inspect her new anatomy. The cock was about average length and thickness, but that was enough to make Yuriko blush.
Yuriko was now a man with only her face still staying girly. She had short hair anyway, so she could pass for a pretty man quite easily.
Her new body felt different than her old female one. She was a little stronger and taller, and she had a deeper voice. Thankfully, the boner that came with transforming disappeared quickly.
"Looking good Yu!" Saya said, calling Yuriko by the nickname that she used when Yuriko was in male form.
Yuriko sighed, "Why Saya? What do you want from me this time?"
Saya replied, "Well Yu. I want you to..."