"And the first person I would like to duplicate is ... my sister," Jon said. The stone glowed and he felt his body change. He felt his penis shrink and get pulled into his body, becoming a vagina. He felt a sudden weight on his chest as breasts developed. It felt indescribably pleasurable. When it ended, Jon stripped off his now poorly-fitting clothing and looked at his new body.
He really was his sister. His body was identical to hers, down to the black hair and pale skin. He liked what he saw, even with the small breasts and the obvious Goth look. But just as he wished, he was his sister's duplicate. And if Zoe was a Goth, then he had to be a Goth too.
And then, as Jon was still looking over his new body, Zoe came in, startling him.