For the most part, I would expect Japan to actually be pretty okay in a disaster like this, all things considered. It isn't really the country where I expect people to start rioting when public order is lost; the beginning of the first chapter seemed much more appropriate—that is, if anything, I would think the problem would be prolonged panicked inaction.
Also, the Japanese government is not so incapable that it can't send runners on foot (or after a little while on bicycles—someone's going to have a fiberglass one around, maybe you'd be stuck with makeshift wooden wheels which might suck, but...) with messages once they got their act together. They might send out bad advice, but the total communications breakdown doesn't make sense.
Some of the older generation should still remember living in a country that was coming up lopsidedly with growing pains; traditional farming and living techniques won't have gone by the wayside, a lot of things missing because of the lack of electricity could be compensated for...
Famine would eventually be a real problem because of Japan's reliance on food imports—they produce only about half(?) the calories they eat—I would expect rationing. And maybe some food theft. But not the sudden anarchy and civil war shown here.