There's lot's of good advice and experience regarding Apple Pay, mobile Suica, and iPhones and iWatches. Let me make a helpful suggestion for those reading this that are not regular travelers to Japan: consider not bothering with it. Consider all of the issues above: what model iPhone or iWatch. Where was it purchased. What iOS version. What region is it set to. Primary support not in English. And so on. Do yourself a favor and just get a regular Suica card upon arrival (takes all of 30 seconds) and be done with it. You won't get any additional functionality by putting it on your phone or watch that will make any difference for a short stay, and you will save yourself a tremendous amount of frustration, research, and worry. You will find that just the regular Suica card has so many advantages compared to whatever you have at home that it will be more than enough of a "wow" factor without having to spend half a day of your visit being frustrated. At least that's the way I see it.