KIX-SFO effectively there is only the UA 5 times weekly flight plus ANA code share. There are many more flights NRT-SFO.
For UA however, at the moment, the newly configured 747 used on NRT-SFO route is minus about 20 business class seats making upgrade impossible. That single KIX-SFO flight is still using the old configuration 777 with better upgrade possibilities. The 2nd daily NRT-SFO that just started again at end of March is also using the older 777 configuration.
The UA KIX ticket counter closes 45 minutes before flight time so the check-in window is very narrow.