Everyone in Japan from 20 to 60 years of age regardless your nationality, must pay into the National Pension Scheme. If you are an OIST direct employee, you will automatically be enrolled into PSMA which is Employee's Pension Scheme.
Please refer to the site: Japan Pension Service.
OIST has a contract with a professional tax accountant who speaks fluent English and also has a mastery of taxation in Japan and tax treaties. If you have any question related to tax issues, please contact at email@example.com. HR will refer you to or seek advice from a tax accountant, if needed.