I took this bag to Japan and stored it in coin lockers at train stations in both Akihabara and Shinjuku (both in Tokyo):
26 inch roller bag (Amazon link).
According to Amazon, this bag is 26 inches tall, 11 inches long, and 15 inches wide. (66cm x 28cm x 35cm).
I took a picture of it in a "large" sized locker. This one was at the Shinjuku station, but the ones at Akihabara were the same size.
I would have had room to put a smallish duffle bag on top of it, and there was also room left over on the side, but (it may be hard to tell from this picture) had my bag been packed any fuller and therefore had been even an inch fatter, I don't think it would have fit.
This bag was too large to be used as carry-on luggage on my flight and had to be checked, but it did fit (snugly) into the locker.
The large locker in Shinjuku was 500 yen for 12 hours. The one in Akihabara was (if I remember correctly) 800 yen for 24 hours.
You need 100 yen coins to use these lockers, so I made sure to save them when I received them as change (although I'm sure you could stop somewhere and ask for change). Insert your luggage, insert your coins, close the locker, and take your key. I assume you would have to insert more coins to free your locker if you stay over the allotted time, but I didn't test that theory!