What are the high seas areas from Shanghai to Nagasaki, Kagoshima and Jeju in South Korea? How big they are! Traveling by cruise, I want to rent Wi-Fi, but I don't believe it.

The area should be as shown on the map. The WiFi you rented on the high seas has no signal, but the ship comes with a rather expensive WiFi. Take Ocean Quantum as an example. The one-day package is 30 dollars a night. You can use it if you don't mind the price. The whole package will be cheaper. The rented WiFi can be used on shore, but it is not common in Japan and South Korea, (╯‵□′) ╯╩┻┻, (PS: duty-free shops can access the Internet)