Chiyo nodded, her jaw tight and her eyes grim. “They will not get the mirror, sister. Not tonight. Never.” She reached into the left sleeve of her haori and pulled out a folded fan. With a flick of her wrist, it sprang open with a metallic whisper to reveal itself as a deadly weapon, its edge honed to razor sharpness. “I have not used my tessen in years past counting, but should the dogs attempt to enter the honden…” Chiyo spun the fan in her furred fingers, its deadly edge splitting the air with a fearsome hiss and blurring from the speed of its movement as she expertly guided it through a complex exercise. In her left hand, her prayer beads glowed with a dull azure light. Then, with a sudden movement, she flicked the fan closed with a sharp click and the prayer beads once again became simple tiny ceramic and wooden balls strung on a hempen cord. Chiyo slid her tessen back up her sleeve.Chiyo, in the story, is a master of Tessenjutsu, a martial art specializing in the use of the iron fan.
And it appears that practitioners of the art continue to keep the martial alive today. Not only can you buy a working tessen on Amazon, but there are videos on YouTube dedicated to the art.
The Japanese never fought with the fan open, preferring to use the fan closed for striking or thrusting. However, the Chinese also used the fan and I found one video that has a truly beautiful kata (training exercise):