Exact documents vary by program (undergraduate vs graduate vs special/non-degree), but common requirements include an application form, academic transcripts and graduation/degree certificates, passport copy/ID, and language proof (English tests for English tracks and/or JLPT/EJU-related proof for Japanese tracks). Some graduate routes also ask for research-related documents (research plan/proposal, supervisor contact, etc.).
Shimane University’s international guidance for entry procedures lists examples of required documents for immigration steps such as an application for Certificate of Eligibility, a copy of your Letter of Acceptance or exam result notice, passport-style photos, a Letter of Financial Support, and “Certification of Japanese Language Proficiency Test” (and sometimes a document certifying your research project).
Recipient example: Ragini Kumari warned to start paperwork early: she said she would “start preparing my documents even earlier,” especially “recommendation letters and SOP drafts,” and she emphasized tailoring her Statement of Purpose to faculty alignment.