Please be aware that Bangkok and Tokyo has multiple airports and that these results are for all airports serving the city.
The best month to fly between Bangkok and Tokyo is September and the most expensive month to fly is April. (Average prices, based on 649 datapoints.)
The best day to arrive at Bangkok is Saturday and it would be best to avoid Monday, as prices are on average 82.66% higher than on Saturday. (Average prices, based on 673 datapoints.)
The cheapest airline flying from Bangkok to Tokyo is Thai Airways. They are 29% cheaper than All Nippon Airways. (Average prices, based on 658 datapoints.)
The best time to fly is at around 2. (Average prices, based on 973 datapoints.)