If given a choice, I think most people (especially Malaysians and Singaporeans) will avoid traveling to Japan in summer as they often have the image of Japan in this unbearable heat during the season. I was one of them.
I had been to Japan in summer several times, late June/early July. It was as hot as KL/SG, but as a traveler you often feel that the heat is worse than the tropical cities because, well, back home we are mostly staying indoor all the time or hide inside a mall.
So yes, I had to agree that, summer was probably not the ideal season to visit Japan if you are not a fan of sweaty activities and hot climate. I avoided visiting Japan in July-September as much as I could. read more