Originally Posted by
CPH-Flyer
They will give you both boarding passes in Boston, and if you have any luggage check it in as domestic connection. But you will still have to reclaim luggage in Narita, and check it in for the domestic flight. Cut off for domestic flights is basically scanning your boarding pass at security 20 minutes before departure.
Even if checked through the risk is your own, and the flight is the last JAL flight of the day. JAL may rebook you for free, but have no obligation to do so. They will not put you up for the night, or pay for the shinkansen if you miss it.
Thank you for the comprehensive repsonse. Looks like I pushed my luck here. I would have to go into Tokyo to catch the train and that just adds more work, so I guess I may have to do the Hilton NRT for the night in the worst case.