If you are coming to Japan as a student you will need a college student visa. You will need to prepare the following:
College student visa
- passport
- two 45mm x 45mm passport-type photos taken within the previous six months (stateless persons must submit three photos)
- two official visa application forms, available at the embassy or consulate
documents certifying the purpose of the visit.
- A copy of a certificate of admission from the educational institution where the person concerned intends to study. In the case where he or she intends to study as a research student or an auditor, documents certifying the substance of the research or the subjects and the number of lessons from the educational institution concerned.
- Documents certifying that the person concerned can defray all expenses incurred during the stay in Japan. In cases where the expenses incurred during the stay in Japan are defrayed by another person, documents certifying the income of the person who intends to defray all expenses and documents showing why he or she intends to defray all expenses for the person concerned are required.
Please check this site of the Japan Ministry of Foreign Affairs for detailed information.