To stay in Japan with any visa a besides tourist one, it is mandatory to have medical insurance during your stay in Japan. It can be private insurance, Japanese public insurance or even both at the same time.
Public insurance is cheaper than private insurance, if not used. But if used (hopefully not) for medical purposes it would only cover 70% of the medical bill. The private insurance terms and prices would have to be discussed with your present insurance contract.
JAPANESE PUBLIC INSURANCE
The Japanese Public insurance covers all residents of Japan and the cost varies but depends on the costs of the previous year.
For those who start working in Japan, as in the case of those who arrive with the Working Holiday visa, the annual cost is approximately € 20 per month, The bills will arrive to your registered address every couple of months. This insurance covers 70% of medical costs. The other 30% would have to be paid by you.
You can acquire your public insurance in the city ward office of your registered address. This can be don’t at the same time you’re registering yourself. Keep in mind that each time you change address, you’d need to register the new address at the ward office, but this will not affect your insurance.
On the other hand, there is the option of hiring a private insurance. This option can be contracted with almost any major insurance company in your country. Depending on the company and the package, the price can vary a lot. There are also travel insurance companies whose policies cover more appropriate problems and whose rates are quite competitive. If you go for this option, you should check the “others” option in the medical insurance section when you fill out your registration form at the city wardor tell the person who attends you in City Ward that you already have private insurance coverage.