Solve 1 or 2 Mathematics/ Physics Questions (on board or on paper) in front of the professor. These questions are similar to what you will receive in the paper based test.
Questions related to your Academic Background, ( basic questions about your high school)
Questions related to your aim, purpose (something like: Why do you want to Study Mechanical Engineering at Tohoku? Why did you choose Japan? What do you want to do after graduation?)
Some social questions like (What is the role of engineers in society ? )
Followup questions based on what you said (for instance you might have answered that you like airplanes in Question 3. Followup questions like: How does an airplane fly? What are the main types of forces involved? )
Lastly, you need to present yourself with confidence. If you do not know answer to some questions, say you do not know, but you still want to try and answer them .

Thanks,
Azim