Star Alliance member Air China has Los Angeles to Tokyo tickets at $540 round trip for late August to October. Most other airlines are over $800.
Google Flights shows lowest fare at $611, but then lower Air China fares pop up in the search results at $548 on Expedia and “Check Price” link for Air China. The Air China ticket price is nearly $10 lower at $539.
Air China Los Angeles LAX – Beijing PEK – Tokyo NRT – Beijing PEK – LAX
There are overnight transit layover options for Beijing, if desired.