I hate the Japanese carriers. Their contracts are longer than those when buying a house! The other week my wife and I wen to AU to change our plan and upgrade my wife to the iPhone X, it was a nightmare and we left before doing anything. Seems they have changed their plans back to the way they used to be, pay per amount of data you use, or pay for a flat 20GB plan. I was pissed and now we are looking at Y!mobile as well as the others. I know they do this on purpose to confuse the customer, but I guess they are just learning from the best, carriers in America.
Check out the new carriers: Aeon, Rakuten, LINE, etc. They are pretty good and 1/10 the price :)
Even buying the unlocked iPhone retail direct from Apple you should be able to save money over the couple of years you'd have been on a contract...