When you write a contact e-mail to a supervisor you wish, better address your e-mail to his/her own name rather than using "Dear Sir" or "Dear Madam," for it sounds like bulk e-mail sent out randomly to many possible host supervisors; it may spoil the chance to receive reply e-mail. Also, specifically declare your research topic or plan rather than using equivocal words such as "the research topic in your lab fits my profile" due to the same reason.
UTokyo has several different statuses for international students and researchers. Clearly show which position you wish: Research Student, MS Student, PhD Student, or Postdoctoral Fellow.
Tell us your research experience. It would be helpful if you would attach your published papers to your CV.
It would also be helpful if you could provide us with a reference letter from your current/previous adviser(s).
Tell us your future plan after your status such as Research Students, MS or PhD.
Tell us your financial plan. Are you a self-financed student, a student on a scholarship program or are you going to apply for a scholarship after admission?