Star Alliance airlines have Los Angeles LAX to Tokyo on sale for travel January through April 2018.
Singapore Airlines appears to be the lowest ticket price at $499 round trip in Jan-Feb and $519 March-April. ANA and United are about $20-$60 more.
Online travel agencies have even lower fares with Expedia at $475 round trip and Momondo.com showing other OTA sites at $468 round trip for Singapore Airlines flights.
Singapore Airlines flights on Expedia.com
Los Angeles LAX – Tokyo NRT – Los Angeles LAX