Answer: As small as possible.
Why am I recommending small luggage set for your trip to Japan? Because Japan is not made for large luggage. I see people struggle with this all the time. They bring one huge suitcase that they might not be able to even pick up only to wish they had brought two small suitcases a few minutes after landing.
Airport
The first time you visit a restroom in Japan will be at the airport. Almost everything in Japan is small and that includes the restroom. Good luck getting a huge piece of luggage in the restroom and if you can there is no room to put it while you take care of things.
You can leave it outside but there is always a possibility it won’t be there when you return. This is Japan and the crime rate is low but are you willing to risk it? Hopefully, you’re in a group and someone you know can watch it.
Cab
You’ll get a cab to hull it around? You must be rich because cabs cost a fortune in Japan. It’s 40 miles (65km) from Narita to Tokyo. If I take the cab to the closest station to my home it cost about $10 for a 4-minute ride.
Elevator and Escalator
You’ll use the elevator or escalator? I hate to break this to you but not every station in Japan has these. If they do there are under repair several times a year.
Stairs
The alternative is a long set of stairs and I have carried luggage up these long stairs several times in Japan. I always want a workout after an 18-hour flight when jetlag is most on my mind. Walking up steps in 100° weather with a huge suitcase is my dream workout. I hope you feel the sarcasm in these statements but I also wanted to let you know what you may be in for.
I’m not talking about 20 steps either, how about 50 or more. 
Trains
Trains like the Skyliner and Tokyo (NEX) (fully covered by the JR Rail pass) do have some space for large luggage but after arriving at your destination you’ll need to ride the regular train or bus.
Regular trains are not equipped to handle large luggage they have small overhead racks and you’ll need to pick up your luggage when getting on and off the train because of the gap between the train and platform.
You’ll also need to keep control of your luggage while the train is moving. The Japanese will be very upset if you don’t. That’s not easy to do if your luggage weighs more than you.
The local bus has no storage space for luggage either. I can take small luggage on a local bus but a large suitcase will not fit. The bus driver will ask you to leave if you are blocking the passenger aisle and the Japanese will not be pleased to have your huge suitcase smashing into them.
Moving to Japan
If you’re moving to Japan you’ll want to ship everything here and just bring a carry-on and small backpack. Have the shipping company deliver the day you arrive or the day after and spend the night in a hotel.
Travel Smart
I don’t see Japan making room for huge heavy luggage any time soon. I wanted to let you know how difficult and expensive it is to get around Japan with it. Using your smaller luggage is the smart way to go.
The alternative is not pleasant but you will likely end up on YouTube so that’s a plus.
Get smaller luggage here.
If you have a question please post it in the comment section below and I will be glad to answer you.
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