Foreign students and researchers who intend to newly enter into Japan are required to apply for a certificate of eligibility (CoE) and a relevant visa depending on the country of their stay before arrival as well as their period of stay in Japan.

You should take any necessary procedures, referring to the guide information provided at the time of enrollment / employment.

Further, if you have received three doses of COVID-19 vaccines validated by the Japanese government and can present a valid vaccination certificate issued by a public institution etc. of the country where you have got vaccinated, you do not need to obtain a certificate of COVID-19 negative test result tested within 72 hours of departure.
※As of 01Mar2023, passenger from China (except for from Hongkong and Macau) by direct flight are subject to hold COVID-19 negative test result tested within 72hrs prior to departure , and take COVID -19 test upon arrival even though hold a valid vaccine certificate.

For the latest information regarding the documents you need to prepare before traveling to Japan and other necessary information after entry into Japan, please refer to the website below.

(Reference)
Ministry of Health, Labour and Welfare of Japan – COVID-19: Current Japanese Border Measures
https://www.mhlw.go.jp/stf/covid-19/bordercontrol.html
Ministry of Health, Labour and Welfare of Japan – Vaccine Certificate for Quarantine
https://www.mhlw.go.jp/stf/covid-19/border_vaccine.html