1.Google: keyword (subject you want to study)+university to search.
The variety and quantity may not be ideal.
2. Go to the university homepage and find your research department one by one.
Find a university ranking and search from top to bottom.
3. Search for papers related to your research topic. Look at the references in the references.
It takes a lot of time, and it is also a question whether we can find a suitable Japanese professor.
# It is best to combine the above methods. For example, first find a professor in this field, then read his/her papers, and then read the papers cited by other professors. However, there is a disadvantage that many research departments cite their own or cooperative research departments' papers. So look for more papers from professors in other schools.