LAX/NRT is generally a "give me." I even typically use LAX/NRT or SEA/NRT as segments to allow an XF award BKK/USA, and then waitlist the rest of the itinerary.

NRT/BKK is tough, often C is full.

Flew BKK/NRT/BKK on March 31, and is often the case, C was full both directions. I was on a Z fare, and got the lucky op-up to F on the BKK/NRT segment.

I do think it fills with upgraders (from watching the inventory on united.com before the my flights), and as a 1K you'll likely get it, but not until just before the flight.