The Japanese student route runs through a Certificate of Eligibility. Your institution applies to the immigration authority on your behalf, and once the certificate is issued the visa application at the mission is comparatively quick. The substantive assessment happens at the certificate stage, not at the consulate.
This means your institution is the applicant in practice, and its internal deadlines govern your intake. It also means the documents you supply to the institution are the documents on which your immigration status is decided.
Financial evidence
Japan scrutinises the source and history of funds carefully, including the sponsor's occupation, income, and relationship to you. The expectation is a coherent explanation of where the money came from, not merely evidence that it exists.
A large deposit with no matching income history is the classic failure. So is a sponsor whose stated income does not plausibly support the stated support.
Language
Japanese-taught degrees require certified proficiency, typically demonstrated through a recognised examination. English-taught degree programmes exist at both undergraduate and postgraduate level and have expanded, but they are concentrated in particular institutions.
Language school routes are a legitimate pathway into degree study and carry their own visa category, but the pathway should be planned deliberately rather than entered as a way of getting into the country first.
Scholarships
Japanese government scholarships are substantial and are administered both through the embassy and through university recommendation, on different cycles. The embassy route in particular has an early deadline relative to the academic year.
Applicants who discover the scholarship after choosing the university have usually missed the recommendation route. Map both before committing.