Transit visa Via japan -shanghai-thailand

If your precise itinerary is:

Japan - Shanghai - Thailand

Then you will be covered by 24 hour visa free transit and you do not need any kind of visa. So, this is not 24 hour transit visa, but visa free transit or better to say, there is no visa of any kind.

If your layover in Shanghai is a longer one, for example longer than 10 hours, you can apply for a temporary entry permit at transit counter upon your landing in Shanghai to be able to exit the airport and to shortly visit the city. This application is free of charge, but you have to be aware that this permit is granted based on a discretionary decision of airport authorities on the day of your arrival. In any case, you will reach your final destination without any visa.