Please be aware that Osaka and Seoul has multiple airports and that these results are for all airports serving the city.
The best month to fly between Osaka and Seoul is July and the most expensive month to fly is January. (Average prices, based on 201 datapoints.)
The best day to arrive at Osaka is Thursday and it would be best to avoid Saturday, as prices are on average 164.09% higher than on Thursday. (Average prices, based on 228 datapoints.)