Is Direct Flight to Hainan a must?

A direct or better say, nonstop flight from a third country to Hainan is an absolute must. You can take a flight from Hong Kong as well. The same thing is valid for your departure from Hainan.

You cannot rely on 144 hour visa free transit scheme because it is valid only if you are in a transit in just one Chinese transit area and with itinerary that has two other different countries as immediate points before and after that Chinese area. Also, Hainan is not included in 144 hour visa free transit scheme.