It is possible to send packages to the Post Office in Tuolumne Meadows (see our Resupply Page: https://socalhiker.net//backpacking/jmt/resupply-addresses/) but it seems like it would be pretty expensive to do so from Japan.
Unless he wants to carry foods that aren’t readily available in the US, I would suggest purchasing in San Francisco.
The other variable is how long the trip is. If he’s hiking for three weeks like I did, he’ll need to resupply along the way, which means mailing to a couple of additional spots.
It is possible to purchase food at Tuolumne, Reds Meadow and VVR, but you’ll have to accept whatever they have at that point in time. They are not full-featured markets and won’t have the widest selection of food.