Almost all apartment leases in Japan require a guarantor (rentai hoshonin), a person who co-signs the lease to share liability (jointly and severally) with the tenant for any debts to the lessor. Generally, Japanese students ask a family member (parent, sibling, etc.) to serve in this role, but since international students often do not have someone who they can ask to be a guarantor, the University of Tokyo may act as your guarantor if you meet certain eligibility requirements.
For details, please see https://www.u-tokyo.ac.jp/adm/inbound/en/life-housing-g.html