Transit free visa

Jean, your itinerary is definitely eligible for visa free transit in Shanghai if your flight from, I assume, UK to Shanghai does not have any additional landing in mainland China or in Japan.

Whether you will be eligible for 24 or 144 hour visa free transit depends entirely upon your entire transit time spent in Shanghai. If your entire transit time, calculated from your scheduled arrival by plane, until your scheduled departure by cruise is less than 24 hours, you will be eligible for 24 hour visa free transit and if this time is longer than 24 hours for just one minute, you will be eligible for 144 hour visa free transit.

In any case, if your flight is eligible as I have explained, you will be perfectly eligible for visa free transit regardless if it is 24 or 144 hour visa free transit and you don't need any kind of visa.

All you have to do is to print out your cruise ticket and have that printout with you. Also, you will declare at check-in in UK that you will travel to Japan via Shanghai using 24 or 144 hour visa free in relation to the entire transit time in Shanghai. Beside the mentioned, you really don't need anything more.

Upon arrival in Shanghai you will approach 24 or 144 hour visa free transit counter where you will apply for a temporary entry permit that will be granted to you because of your itinerary.