Portable Wifi needs a sim inside. These are different countries, so you need different sim cards to prevent roaming.
I was going to China and Hong Kong this summer until my step son couldn't get a Chinese visa. Now I have 2 prepaid SIM cards available for fast 4G 3GB data and voice for China and Hong Kong. These are good for 7 days and can be topped up/extended via their website. The SIM goes through Hong Kong so banned sites like Google are accessible. The SIMs are still in their original un-opened packages and can be activated once in China. After inserted into the phone, when the phone is turned on, the SIM is activated. These SIMs must be activated by 9/30/2018. I paid $18 each which includes shipping from eBay. If interested, I can ship them to you for a cheaper price - you name the price but it has to be reasonable. As a bonus, these SIMs also work in South Korea. So you could visit the DMZ line when they open North Korea. I didn't find any SIMs that could work with Japan and China because, like you, I wanted a SIM that could go throughout Asia. This was a good alternative. If interested, respond to this message in this forum.