2 days in Shanghai , cruise to South Korea , then cruise to Beijing for 3 days then on to Japan

Tony, if you fly to Shanghai from a country other than South Korea, and you don't have other stopovers before arriving in South Korea, you can enjoy the 144h visa-free transit in Shanghai.

For the layover in Beijing, if the route is South Korea - Beijing - Japan, then you will be eligible for the 144h visa-free transit in Beijing.

Therefore, no visa is required.