It's just an ordinary, if large, paper fan -- accordion-pleated white paper, taped at one end to form a handle. But some characters wield them the way others do the dreaded Hyperspace Mallet, and get much the same results -- the unfortunate target usually goes rolling down the street from the force of the blow. This may go back even further though, since fans with sharpened metal ribs were allegedly used as weapons of war and assassination, being particularly suited to the latter due to ease of disguise. (In fact; there are arts about using fans, as well as fans made for weapons.)