Tokyo experiences its rainy season from late June through July, so pack your umbrella and some quick-drying clothes. In 2006, my trip to Tokyo was a week long and I did not see my shadow at all because the clouds were so thick. Worse yet, it rained (sometime heavily) about 80% of that time. I had plans to climb Mt. Fuji (a lifelong gopal) that I had to defer because it would have been an unpleasant, viewless seven-hour uphill slog and an equally unpleasant downhill. Sure, I would have been above the clouds for sunrise, but to see WHAT?!?!? Just Clouds?!?! No Thanks.
Interestingly, all the Tokyoites I talked to insisted that the weather would clear by 1 August. Unfortunately, I don't know if it did because I was gone by then.
Miscellaneous: Luckily, Tokyo has lots of indoor activities or sites that can be seen unimpeded by rain. Given my rainy calendar, I chose to check out several museums that I had passed by on other trips, such as the Mori Art Museum, the Museum of Photography, the War Museum at the Yasukuni Shrine and, of course, the Beer Museum at Yebisu Gardens (after which I didn't care about the weather!). So, even if you have to be in Tokyo in July, you won't be bored.
Luggage and bags:
If your in Japan make sure bags or luggages you buy are seam sealed and the zips are waterproof. Weather in Japan especially in the monsoon season could rain at anytime without warning and at a sudden.
Clothing/Shoes/Weather Gear: A good windproof rain jacket would be best suited to the monsoon season of Japan, as it can suddenly rain. I was there for 3 days and it rained every single day.
Miscellaneous: If you would like to buy a cheap umbrella, visit the 100-Yen shops all over Japan. They are like discount variety stores and everything in the shops is 100 yen. 100 yen = AUD$1.13 or US$0.85
Clothing/Shoes/Weather Gear: if you plan to visit Japan and tokyo during the fall season, you better bring umbrellas and rain coats or other rain gear handy as this is also the time of occasional thunderstorms and showers and even in the summer season, they have the occasional thunder storms hence umbrellas are a must and you can buy them at any convenience store if you did not bring any rain gear and they are available in short and portable kind and the long, like a walking stick kind. prices are 800 yen for the short umbrella and 600 yen for the long umbrella.
an umbrella is very important thing, in April you need summerclothes but sweater and jacket too
Photo Equipment: photocamera is highly recommended