I want to Travel from Fukuoka, Japan to Shantou, then return to Sendai, Japan

There is no direct flight between these two places. You are suggested to take a flight to Shanghai Pudong Airport first. Then transfer to a flight to Jieyang Chaoshan Airport. After arriving, there are many direct coaches to the destination.

If there is seasonal flight to Guangzhou, you can fly there too and then take a bus to your destination.