When is the cheapest time to travel to Japan in a year?

Travel to Japan 1 1~ February of the following year is the peak season for winter travel in Japan, especially the Hokkaido line. March-May is the peak season for viewing cherry blossoms and 9- 10 is the peak season for viewing red leaves. June is relatively cheap, because there are no seasonal hot spots, and the weather is getting hotter and hotter. There will be a summer vacation in July and August.

So on the whole, June may be a cheaper season.