Well they say the rainy season in Japan is in June, but that’s not technically true as it rains quiet a lot throughout the year. It might be a good idea to not only have an umbrella cause it’s also windy quiet a lot too. And, those umbrellas really don’t stand a chance under those predominant weather patterns that occur here. You might be better off investing in a really good rain coat Also, having great rain boots won’t hurt either as most places require you to take off your shoes. You really don’t need the problem of placing wet socks into slippers..