Students that want to do their internship in Japan need a general visa. The general visa is valid for up to 2 years and can be applied for at the Japanese embassy in your country. In most cases, the visa is free for interns but it can take up to two months for the visa to be approved.
When applying for the general visa, you are required to submit the following documents.
Check with the international office at your university if they are qualified to give you a Certificate of Eligibility. This document will speed up the application process significantly.