Professor asking me about my financial condition
Dear Professor X,
  
  Thanks for your email.  Regarding your question about financial support, I am planning to apply for a MEXT scholarship.  If I receive this scholarship, it will provide me with [explain the terms of the scholarship].  Would you be willing to support my application for this scholarship?  If so, I would need [explain what you would need from him].
  
  If I do not receive the MEXT scholarship, I would plan to finance my graduate education by [explain your backup plan].
  
  If you are aware of other funding opportunities, I would be glad to hear about them.
  
  Sincerely,
  
  [your name]