From within Japan there are 5 – 7 flights per day from Tokyo (Haneda Airport) and 1 flight a day from Nagoya. However, JAL and ANA are the only carriers that operate flights to Asahikawa so prices are not exactly cheap.
※ If you reserve a ticket 1 – 2.5 months in advance you can get a much cheaper “early reservation discount”. And if you can’t get a discount ticket, it’s cheaper to fly to Sapporo via a budget airline or LCC, then take an express bus or train to Asahikawa.
International flights from Taiwan are available from budget airlines such as Tigerair Taiwan, operating 2 flights per week.