Will these giftcards work worldwide or are they reserved to users from Japan and China ?
If they work worldwide, I would suggest to provide a few vouch copies which will boost your sale. If they are reserved for Japan or China, there are local boards in Chinese and Japanese, you can try your luck there.
only for japan my friend, but only change country in you google account and you can redeem the code. I do not know any board of japan, If you can give it to me, I would appreciate it a lot