I read once an one-shot shoujo manga about a girl who met a boy dressed as a rabbit (I can't remember well, I think he had some kind of job to dress up in that rabbit outfit for kids). He didn't talk at all but he and the girl became friends and talked by writting in a notebook. Later on it was revealed that the guy was a mute (at least that's what I remember).

I really loved that manga but it was so long ago, I can't even remmeber if it was a side one-shot or part of a one-shot collection.