I think lots of people have already said this, but I'm sort of disappointed at the lack of apparent consideration for just how much of a resource emergency they would be in. Like people still casually using cars in Ch. 2, as if no strict resource rationing has yet been put in place (as one does when one's country is cut off from resources, e.g. when blockaded).
Food would be priority number 1 by a mile and a half, it's true—but Japan wouldn't be cabable of maintaining it's technology stack when cut off from the rest of the world—I want to see people scrambling to figure out how to develop and obtain alternate fuels that are "good enough" to run in existing engines, filling in the gaps for stages in manufacturing processes that were outsourced 'till now, start scrapping old sources of materials for stuff that Japan can't mine itself... that sort of thing.
There would have had much more impact in Ch. 2 if, for instance, we saw people lining up for petrol rationing lines (possibly shielded from the view of visiting dignitaries). Instead the highlight of the chapter was the humorous visual juxtaposition of a medieval chap reclining on a cruise-liner pool deck.
This comes within inches of being a truly magnificent thought-experiment, yet so far is missing the mark completely for me... it's frustrating. And it's not like there's great character drama or anything that I'm supposed to be focusing on instead :/