Hokuriko Shinkansen Tickets

I will arrive in Tokyo on December 31st and need to make my way to Kanazawa. At the moment I do not plan to travel on a Rail Pass.

JR East allows me to buy tickets online and make a seat reservation between Tokyo and Jōetsumyōkō. How do I get a ticket between Jōetsumyōkō and Kanazawa? I do not want to wait until I arrive in Japan because I expect it to be a very busy day for travel and would like to travel in Green Class or even Gran Class. So how do I go about getting a ticket for the entire journey?

There is also a small probability that I will purchase a Green Class rail pass. But the problem of getting a seat reservation for the full journey is the same. In the event that I would like to upgrade to Gran Class, will JR East allow me to pay the fare difference between Green and Gran Class? Would such an upgrade only be possible in person once in Japan?

JR West, the owner of the latter portion of the Hokuriku Shinkansen, doesn't allow reservations outside of Japan. You must buy the ticket in person when you arrive.

JR East allows me to buy tickets online and make a seat reservation between Tokyo and Jōetsumyōkō. How do I get a ticket between Jōetsumyōkō and Kanazawa?

This is definitely a problem with the online systems as they are. It's also a relatively unusual case, so I'm not exactly sure how they handle the situation on the train. In light of that, I'd suggest contacting a travel agent and purchasing the ticket through them.

In the event that I would like to upgrade to Gran Class, will JR East allow me to pay the fare difference between Green and Gran Class?

No, in that case only the base fare would be covered. You would have to pay the full Gran Class and shinkansen supplements instead of just the difference.

Thank you for the replies.

The problem with "fragmentation" is definitely an area where the JR companies and the Japanese travel industry as a whole needs to improve, especially now that boosting foreign visitors is so high on the agenda.

Travelling with JR on the ground and making reservations across the JR regions works flawlessly in the country. Why is it made unnecessarily difficult for foreigners? Same applies to the Japanese airlines and their domestic/international silos when it comes to reservations. You would have thought that a few clever IT people could unify these silos, at least the customer facing side. The separation could be maintained for the airlines' internal processes should they feel that it gives them so many distinct advantages.

And don't get me wrong, there are many things I like about travelling in Japan. I am still hoping for IATA to endorse the domestic boarding pass format internationally.