It gets a bit complicated, because some of them need a Japanese mobile phone number, but they are straightforward IF (and this is where it gets even more complicated) you have the code (like an old videoplus+ number) from one of the listings magazines.
Shop staff are very helpful though, if you take a few screenshot of what you are after (not many people, especially men, speak good enough English to understand fully what you’ll be after)
This sums it up better than I can: