Hong Kong Express Airways is holding ”Pay To Go, Return For Free” from February 14, 2017.
As for this sale, an return flight is free.
・The Japanese route
Sale period: Feb 14, 2017 – Feb 16, 2017
Travel period: Mar 1, 2017 – Dec 31, 2017
Round-trip airline tickets from next month to the end of the year will be substantially half price.
Since return flight is free, the sale must be reserved in round-trip.