An Uchiwa is round paddle-shaped paper fan used in Japan for fanning rice to be used for sushi.
It can be a fixed one of paper spread out over a frame, or a folding one, or even a regular paper fan not dedicated to kitchen use.
There is no set rule about how long to fan the rice for: some say fan for 5 minutes, some say 10 to 15 minutes. Some advise to fan while mixing the rice, others say that fanning after mixing is fine.
Some more progressive souls will even use a handheld battery-powered fan, or or an electric fan set nearby on low.
Any fan, electric or manual.