If you order a round-trip ticket from AirAsia, departing from mainland China, such as Guangzhou, Shenzhen, Hangzhou, Tianjin, Guangxi or Hainan, etc., the price will be based on RMB, so you will not have to pay for it. There are handling fees and exchange rate differences.
If you order a ticket departing from Hong Kong, Macau or Kuala Lumpur, the fare is not priced in RMB, so there will be exchange rate differences and credit card handling fees when purchasing with a credit card.