I've grown to like twinning stories more and more through the years and it's surprising that I haven't really clocked that before as some of my earliest crossdressing fantasies involved the girls in my school turning me into their 'twin' or having to 'fill in' for them in class. I think it's the idea of becoming like someone else and having to take on their mannerisms.
This is a fun story that I came across recently involving twinning:
This is a rather innocent tale, not really done out of malice and Amy just comes across as a normal, fun loving woman rather than a controlling bitch or bully looking for an apprentice and in fact Dan comes across rather snobby. The change seems to be a pre-break up kindness to him which I'm not sure of but it's a fun tale. I love the rather slow change mainly shown through his reactions as the two converse and I would have liked more description of his clothes changing but that's just me.