Not to hard to download from Japanese App Store.
Sign out of your current current account then Change region. After you do that click to download any "free" app.(this step is inportant otherwise you have to actually have Japanese payment method) Then when you are prompted to make an new account no payment option is available. Then you'll be able to input just the address/location part only. Just use you gps to find a location. (You can get accurate zip that way) I used "Grand Hyaat hotel Tokyo" as the instructions I followed suggested. The Prefecture as Tokyo. You can also use 08 5555555 as the phone number it just has to have the right area code. I think that's it I'm doing this from memory so let me know if I missed something. It's pretty simple there are a couple methods I found online this is just what I felt was the simplest method. I got it done within 15-20 min. It would have been faster but if you put in your age wrong Apple locks you from making an account on whatever device you're currently on. I had to switch back and forth with my laptop to fix the problem.