I have purchased 4 tickets from HIS korea office.
HIS is one of the biggest travel agency (budget oriented), and its branch is in Korea.
I am sure they speak English.

Good points for this ticket:

Change return date without fee
Can stop over in Tokyo up to 14 days
Can use code share AF flight, so chance to ride B380 aircraft
Upgradable from C to F

And price, almost same as Y fare from Tokyo to Europe, especially with surcharges.

Thanks OP for this information.