Social Insurance is a broad term compromised of Pension, Health, Unemployment and Worker’s Accident Compensation [2].
WIP
For most individuals you'll ever be on the NHI (National Health Insurance 国民健康保険) or on the company health insurance (健康保険).
When you are on the NHI you are directly under the state health insurance.
As of 2017, 35,000,000 people are under the NHI directly (28%). While 76,650,000 people are under company health insurance 1.
But there is a catch, most people on company health insurance are actually under National Health Insurance Association / Association Kenpo (国健康保険協会 / 協会けんぽ), this is what the company uses as their insurance in the back. So you are still technically under a state founded insurance.
Some companies instead use an industry wide labor union's insurance (健康保険組合).
Health insurance in japan is extremely regulated and all insurances have to cover a long range of illness so you shouldn't have to think too much about it.
If you are independent you still have to pay for health insurance, but this time you have to pay the whole amount yourself.
You have a few options:
- Subscribe to the NHI.
- If you just left your company you can stay on your previous company health insurance for the next 2 years (it's usually cheaper so it's recommended). This process is called 任意継続保険制度.
- Join National Health Insurance Association (国民健康保険組合) https://www.kyoukaikenpo.or.jp/.
This is usually cheaper than NHI (around 2 mans). But you have to check the conditions as there are requirements for each insurance union. A non exhaustive list of these kenpo hokens:
Under NHI you are required to pay 30% of the medical costs of care at clinic and hospitals. 90% of hospital and clinics are supported.3
Note that also covers you overseas, but only for emergencies, and I would not count on it too much personally.
NHI reimburses Overseas Medical Costs only when they are for emergency treatment. NHI does not reimburse medical costs on trips made overseas for the purpose of receiving organ transplants or other treatments not covered by NHI in Japan. source)
You can get more info on what is covered or not here
Sources:
[1] https://www.kenporen.com/health-insurance/m_knowledge/
[2] http://www.htm.co.jp/payroll-social-insurance-practices-japan.htm
[3] https://japanhealthinfo.com/japanese-healthcare-services/japanese-health-insurance/
[4] https://yosida.com/forms/nationalins.pdf