This is an Edo-period Japanese war fan from the first half of the 1800s, made out of paper and lacquer, and — the active ingredient — iron.
Folding fans had been a part of Japanese aristocratic culture since the 600s. The paintings on them, the gold or silver foil that adorned them, and the mannerisms with which courtiers could carry them (or flirt with them, as the case might be) all made the “Sensu” folding fan a hallmark of the elite.
Although fans were functionally designed to stay cool, they developed a martial purpose during the centuries of the Medieval samurai. They were often used on the battlefield for signaling (a type of solid open fan called a “Gunbai” was often employed for this).
They might also be stashed in the clothing of a samurai who could take them to places where weapons were not allowed. The “Tessen” fans which had outer spokes with heavy iron plates typified this purpose. They could act like small shields to deflect knives, and could be thrown. “Tessenjutsu” evolved as a martial arts with war fans. It had/has a defensive style to it, which makes sense if a samurai needed to use it in a place where overt weapons were banned.
Sources: “A Japanese fan became a deadly weapon in the right hands,” _Ancient Origins_ 30 Nov 2021, Rey Martin. Wikipedia “Japanese War Fan”. Image from auctioneer Pamono, TS-1191460
