Skyteam Alliance member China Eastern has a very low ticket price for Seoul at $379 or Tokyo $409 round trip, but only if you are looking for a two month April to June trip. These low priced flights book in China Eastern economy Q class, a booking code that does not earn miles in any frequent flyer program. I saw some routings where there were Economy B fares for the short haul intra-Asia flight. China Eastern B fares earn 100% flight miles with Delta and most SkyTeam Alliance programs.
Departure dates for these fares are in April with a return in June, so this is only a deal for the long stay traveler.
Delta and United have fares for about $200 more round trip for shorter stays.
San Francisco SFO – Shanghai PVG – Qingdao TAO – Seoul GMP
$379.40 April 19 – June 20
San Francisco SFO – Shanghai PVG – Tokyo NRT
$408.46 April 19 – June 21
There are several low fare departure dates in April. A return in May is a $700+ ticket price. Stay 60 days and the price drops to $408 for some return dates in June.
The round trip fare is $430 with these flights. Change the trip dates to the following weeks for the departure and return flights and the fare drops down to $408 round trip.