What to wear in late May?

Hi, I'm from Singapore and looking forward to my upcoming trip to Japan from 20th to 29th May! My partner and I would be covering areas such as Nikko, Tokyo, Osaka, Nara.

Would love to get some advice on what to wear in late May. As Singapore is a really warm city and we usually dress simply, both my partner and I mostly have only shorts, bermudas as our basic attire in our wardrobes!

Would these aid the weather in freezing us?? What are some of the suitable clothings to bring? And are slippers acceptable in moving around in Japan, as we are visiting shrines and temples as well?

We're pretty much backpacking for this trip so hopefully we can pack light and all, if possible! Would appreciate all your help!

Some average temperatures to expect:

Nikko (higher elevations):
Average daytime high: 16 degrees
Average nighttime low: 7 degrees

Tokyo, Osaka, Nara:
Average daytime high: 25 degrees
Average nighttime low: 17 degrees

By "slippers" do you mean flip-flop type beach sandals? Slippers are indoor footwear in Japan.

If you mean beach sandals, then they are okay, but from my experience people tend to step on the back of them in crowded trains and stations. They are not ideal if you plan to do a lot of walking somewhere like Nikko either, as there are a lot of steps- better to wear something more sturdy.

Search out a good weather site on the net and look in detail. Japan can be very humid in late June. I would bring summer clothes with a lightweight jacket for the cooler places ( Nikko ) and maybe at night. As advised some reasonable shoes for walking on uneven stairs and pathways. Sandals with toe protection would be fine.

Wear the most comfortable clothes as much as possible. Nikko is a cooler place, but you'll be sweating with all the hiking. So, a windbreaker or a thin jacket is preferred, one that can be easily removed. Japan is a sunny place, but make sure you have an umbrella just in case it rained. The transparent one is trendy and you can buy it for around 300 yen. Check the weather always!

As for footwear, I admit I wore flip-flops while touring Japan last fall since it's the most comfortable for me. Though, people sometimes stare at my feet, especially while riding the trains or subway. Heck, I even climbed the Fushimi Inari stairs with it. And yes, get a very sturdy footwear since you will seem to do a lot of walking.

Hey thanks all! Appreciate all your help! =)

If I don't wish to stand out too much in Japan in June, what is the best thing to wear for guys? I don't wish to appear obviously as a tourist.

Why worry about looking like a tourist? You are one, and if you have a camera, a guidebook or luggage it will be hard to hide anyway. Just dress comfortably, and don't worry about blending in.