There’s great fares available from LA to Tokyo from September till early December and also from January to March of 2019. If you fly during weekdays, you’re to get some sub $400 prices for a round trip, non-stop flight, which is an amazing price and probably one of the cheapest ever.
To search for dates, you can try Priceline or Momondo. The round trip shown above is just $387. Tickets are issued by United but you will fly with ANA, which is a great airline. Keep in mind that these prices are for Economy and this is a long flight.
Maximize this offer by using Amex PRG, Citi Prestife, or Citi ThanYou Premier for 3x back on airfare.