Delta Airlines has the lowest fare I have noticed this year from the big three AA, DL, UA for Los Angeles LAX to Tokyo Narita NRT or Haneda HND airports. These are nonstop flights and the cost to fly Haneda is 50 cents more than Narita.
Departure dates: There are about half the dates in November available as low fare departure dates and into beginning of December. Mid-January to March 17 offers the $615 Delta fares most dates. There are China Eastern flights $617 fares into mid-May.
China Eastern, a Skyteam Alliance member airline and Delta partner, has had lower fares in the $500s for LAX-Tokyo, but that routing takes you all the way to Shanghai PVG China and backtracks to Tokyo.
Delta Airlines Los Angeles LAX – Tokyo Narita NRT
$614.70 Tuesday January 12 – Tuesday January 19
Base Fare = $530; Flight miles = 10,932 miles.
Delta Airlines Los Angeles LAX – Tokyo Haneda HND
$615.20 Thursday March 10 – Thursday March 17
Base Fare = $530; Flight Miles = 10,975 miles.