On average, we have 105 rainy days with more than 1 mm of rainfall in Tokyo.
The following figure shows the number of rainy days by year in Tokyo.
In 1890 we had the most rainy days (145 days), and the number of 1943 was the least (73 days).
I do not think there is a trend in terms of the number of rainy days.
The figure below shows the number of rainy days by month in 2013.
Source is Japan Meteorological Agency.
都府県・地方を選択 > 地点を選択 > 年ごとの値を表示 > 詳細（気圧・降水量）