I have no idea whether Japan Post or other foreign postal services can do something similar, but the USPS can hold your mail for 3 to 30 days if you go on vacation. You just need to fill out a simple form at your local post office (or
online), and you can have the mail delivered or pick it up when you get home. I do this whenever I go out of town for anything more than a long weekend. I'm posting this too late for it to be of use to forgetmenots (if it would have been of any use at all), but it's something for people to keep in mind for future eventualities.