Switching the conversation to an economic standpoint Japan and South Korea are high tech leaders, they designed stuff and shipped elsewhere to build - so their demographics didn't hurt them as much - up till now at least.
China's economy is built on foreign investment and cheap labor, and there loosing both at the same time. They have been trying to expand their capability but so far haven't shown any ability other than to copy whatever someone else made. Possibly that changes but it hasn't yet.
With this point in mind Japan will have the edge as they have adopted automation and robots to a greater extent than China. That is in part because of the older demographics.
A typical Japanese restaurant, you order your food at a kiosk machine and pay with smartphone or card. A robot delivers the food. Some places have robotic cooks for certain tasks.