Those staying in Japan for a year or more are obligated to enroll into national health insurance (cannot withdraw from obligation). When visiting medical institutions, you will be exempt from 70% of medical and pharmaceutical fees by showing your "insurance card."
National Health Insurance Division at the municipal office (after completing alien registration)
If hospitalized for a long period and the expenses borne by the insured for medical expenses for a month or more (the 1st to the last day of the month), costs (except for hospital bed fees, meal fees, medical expenses for health insurance outside of the treatments) that exceed the fixed amount (35,400 yen) will, in principle, be refunded after filing a claim.
After 3 months of receiving treatment, a notice for file ("Notice of Determination for High Medical Care") will be sent directly to your address from the National Health Division at your municipal office. Follow the instructions to complete the process.
The National Health Insurance Division at the municipal office you completed alien registration at.
In the case it is difficult to pay the full amount responsible (30% of medical and pharmaceutical fees), there is an "entrusted payment" system to pay only the amount responsible for with approval from medical institutions beforehand. Designated procedures are required at the National Health Insurance Division at the municipal office you completed alien registration at.