In my research for the trip in Japan, I researched travel in Japan.  The research says that the #1 rule of  travel in Japan is to not rent a car, and the corollary is to not drive in the countryside.

So on Day 4 I took the airport bus back to the Narita airport to rent a car for some countryside driving.

What made this possible was an excellent navigation system in the rental car, which the rental agent configured for English and my initial destination before I left!