Japan, May vs June/July

Hi there,
I am trying to figure which would be best, visit Japan in May or in June-July, considering weather, hiking opportunities, crowds, festivals, etc.

I only know the rain period passes Japan during June-July in most parts, that's all.

Not really sure when to go actually.... Sorry for the hard question

May.
There is a rain season in June, and after that things get hot and humid quickly.

Not really sure when to go actually..

If you decide to visit Hokkaido, July would be best.

Hokkaido: July
Practically everywhere else: May

Reasons, rainy season and hot humidity afterwards

Enjoy your trip to Japan!

So Hokkaido is too cold in May? Is there anything to see in May in Hokkaido or just cold and snow?

It's not too cold and snow has melted by then. But if you are asking about the best time of the year to travel to Hokkaido that's July. While May is simply great for the rest of Japan.
So essentially if you travel in Nqy you can go everywhere. In July it's best restricted to Hokkaido because of the heat and humidity elsewhere.
Roughly speaking.

I was mostly thinking as I have never been to Hokkaido, but if it is cold, and if rest of Japan is muggy when Hokkaido is fine... I would rather go in May really.

Hey, May is definitely worth it, especially if you go very early in May. I had stunning weather, almost too hot (but just almost) along with some foggy and 2 rainy days on an 11 day long trip.

Just note that the first few days of May are a busy Holiday.

Just for that reason I try to avoid early May. I don't really fancy having to share transport and hotels with millions of local vacationers...

What is the weather like in early June compared to May? Is it a big chance of heavy rains?

What about Okinawa region, would May or June, or July be better?

It depends on how well you tolerate heat. I thought mid May had perfect weather - cool to cold in the mountains, pleasant elsewhere. Early June can be very hot in places like Tokyo and Kyoto.

By mountains, do you refer to some specific areas or so?

I was looking into Takayama alps (snow corridor), the Rishiri Island (not climbing ) or even the Nantai in Nikko. If it is snow or too cold I would rather go in summer if so.

But then again, if everything outside of high mountains are too hot ... Is it worth going to the alps in May or would I need to carry a thick coat? Haha...

Hi Peter
Essentially you need to make first a list of places you want to visit and judge your own ability to withstand humid heat. Then we can advise better which time of the year is best. But essentially even in the Japanese alps in summer it is warm, bordering hot.
I went to Hokkaido (Furano and Shiretoko) at end of July this year and one day in Furano I found too hot. But overall the temperature was great.

If this is your first time to Japan I would however advise to start with the more traditional destinations. E.g. Tokyo, Kyoto... as this will give you a nice introduction to Japan. Hokkaido is simply very different from the rest of Japan, having been colonized only about 150 yrs ago and having a quite different climate.

If you opt for Honshu,Kyushu, Shikoku then you definitely will want to go in May. Just exclude the very first days of May and arrive when Golden Week has finished. Although I have to admit that traveling during GW is not as bad as it is being painted.

If you want to add in the alps you can definitely hike in may. For hiking you will in any case need to bring some more specific clothes as mountain climate all over the world is variable. But if you just want to see Takayama or Nagano no coat will be required in May.

Actually I have been to Japan in October as well but had difficulties with several typhoons. But I have been to the "standard destinations" of Kyoto and Tokyo. But I don't mind doing Kyoto again. Tokyo is a bit too big for me though and I think I'll pass it this time for some other sights.

But still I am curious about some outdoor destinations. But if the weather is worse in June/July than in May, even in the mountains. Well, I don't fancy hiking in 20-25 degrees or more and heat and humid. I think that would bring down my walking pace. But I also feel like seeing the alps as well as I couldn't go very far last time :(

I have made a list of want to see's as you mentioned, not presenting it here but seems like 50:50 decision really... Wish I could go May-July or something but that would be too expensive.