One or two doesn't matter. Generally, the customs will not take care of it when going through customs, as long as it is not dangerous goods. But you'll see it when you enter the customs. If you bring it from Japan to China, China Customs will certainly have no problem. If you fly from China to Japan, you need to think about it. But last time my friend bought dozens of pirated CDs from China and went to Japan. Only a few people who were investigated were particularly unlucky.