What happens if I get sick or hurt in Japan?

Tell your host family, dorm manager, or student coordinator immediately. If needed, the student coordinators will introduce you to a local doctor.

Tell the doctor of any medication allergies.

Pay in cash: you can get reimbursed by your insurance company when you get home. If the treatment cost exceeds about ¥30,000, get a doctor’s certificate while you’re there. You won’t need one for reimbursement if the cost is below that amount. The doctor’s certificate itself costs around ¥3,000 to ¥5,000, and treatment may cost less than that. (Thus, good to have at least ¥35,000 in cash on hand for emergencies like this.)

There are several English-speaking doctors and hospitals in Tokyo. This U.S. Embassy page shows medical resources in Japan.