It is not raining, it is simply the popular umbrella in Japan, protecting you from the UV.
Most of Japanese women carry them because, unlike European women, Asian women refuse to have tanned skins and do anything to protect their “white” colour.
But today it was so cloudy that not even a single ray of sun was there, so why the umbrella???
Maybe even the eventuality of seeing the sun is enough! ===> Seriously? -__-“