Honestly they'll most likely choose a safe country where tourists are treated well (i.e. Safe, modern, and non controversial), so no 3rd world countries which rules out the entirety of South America, Africa, Eastern Europe and the Middle East. Next on the list, they need a place lots of people are familiar with, so say goodbye to Idaho and the other 44 states that aren't Texas, as well as things like Estonia and Canada cause Japanese don't know them. Lastly, the region needa a distinct shoreline to allow for an interesting design and geography. This leaves us with tropical pacific islands, Eastern and Southeastern Asia, Australia, New Zealand, and Central, Southern, and Northern Europe. Maybe Vancouver too if GF wants something exotic.
My bet on the near future is either Sicily, Hong Kong, or some parts of Scandinavia or Great Britain. Mostly betting on Scandinavia cause Japan likes blond, tall people that drink milk, plus we need a proper cold region. It could be to Sinnoh what Alola is to Hoenn.
