Transit japan

Formally, you are supposed to fill out the Health Declaration Form, although even this detail becomes obsolete. You will be allowed to transit China even without it, but you may be required to present it by check-in staff at the airport from where you will depart to China. If they require, you will just dedicate 10 minutes to accomplish that right before your check-in.

So they will provide me with the health declaration form if I need it ?
Do I need any sort of 24 hour visa entry or exit permit ?

Yes, you can get the form at the airport. No, you don't need to apply for any permit as you are not planning to get out of the airport.