Upgrade "Visit Japan" sectors?
 

My travel agent was able to use the "Visit Japan" fare (basis "YOKOSO2") for my two domestic sectors within Japan. IIRC, the OneWorld page for the Visit Japan fare said something about upgrading for Y1,000, but I can't find it now.

The JAL web site has a page about "Class J" for domestic flights that says it is Y1,000 extra.

Does anyone know how this works?

I'm flying LAX-NRT on AA, then NRT-ITM on JL, and on a different day HIJ-HND on JL.

You can pay 1000 at check in at JAL Dom counter on the day of your flight.
This will apply only to Class J, not JAL First Class domestic.