Please be aware that Taipei and Osaka has multiple airports and that these results are for all airports serving the city.
The best month to fly between Taipei and Osaka is February and the most expensive month to fly is January. (Average prices, based on 319 datapoints.)
The cheapest airline flying from Taipei to Osaka is Tigerair Taiwan. They are 65% cheaper than EVA Air. (Average prices, based on 327 datapoints.)
The best time to fly is at around 13. (Average prices, based on 367 datapoints.)