I honestly can't stand humidity and extreme heat - Summer is my least favorite season, and I know Japan gets quite humid in the summer. So that's a big no-no for me. I'd probably prefer to go when it's snowy actually, because I want to visit Tokyo and Sapporo especially, and I hear they're quite beautiful during the winter time.

Thanks for the info though.

I've been to Tokyo in December, and it was perfect. Except for 3 days, there was beautiful blue sky and 15-20°C. It was just perfect.

I'd like to visit Japan for a small vacation someday to buy a batch of retro games and see Japan for what is it but I don't even have a passport (European ID instead which is only usable within EU).