Please be aware that Seoul and Tokyo has multiple airports and that these results are for all airports serving the city.
The best month to fly between Seoul and Tokyo is August and the most expensive month to fly is September. (Average prices, based on 434 datapoints.)
The best day to arrive at Seoul is Wednesday and it would be best to avoid Sunday, as prices are on average 37.1% higher than on Wednesday. (Average prices, based on 506 datapoints.)
The cheapest airline flying from Seoul to Tokyo is Air Japan. They are 62% cheaper than Japan Airlines. (Average prices, based on 465 datapoints.)
The best time to fly is at around 14. (Average prices, based on 709 datapoints.)