Japan Student Visa Extension

College Student visa is valid for either one or two years.
To extend the period of stay on your visa, you need to apply for the extension at the nearest Immigration Bureau by the date of expiry.

According to Tokushima University website, extension application is accepted from two months prior to the date of expiry.
According to the officer at Komatsushima Port Immigration Office, extension application is accepted from three months prior to the date of expiry.