Mark felt himself shrinking, and shrinking. He was expecting to grow smaller but not this small. He was also expecting to grow breasts. He did feel his hair growing longer, other subtle changes but...wait...why was Anna giggling so much.
"Anna?" He asked, hearing his voice break. He felt a distinctive twisting in his groin and groaned before he could ask ...he felt his manhood being converted...but still he was not what he expected. He was staring UP at his girlfriend.
"Anna!" He gasped, in a now high voice. "What have you done!"
Anna chuckled and fetched a mirror. "What do you think...."Kate...?"
Mark shivered as he heard the name. And stared at his reflection. Anna's 12 year old sister Kate stared back at him....