Your company will typically apply for health insurance on your behalf and deduct a monthly sum from your salary for it. This type of insurance is simply called kenko hoken (健康保険).
After your employer completes all the necessary procedures for applying for a health insurance, you will receive a health insurance card called a kenko hokensho (健康保険証), which you should keep with you at all times.
To apply for the national health insurance, you will need:
A valid Japanese ID (residence card with your postal address written on it)
Hanko (Japanese seal or stamp)
My Number card if you have one issued (if not, you may be required to issue one simultaneously)
Once you apply for a national health insurance, your application is typically accepted right away and you will be issued a health insurance card typically on the same day. Again, carry this card with you at all times. If you have this type of insurance, you will have to pay monthly premiums by yourself. These premiums are based on each individual’s age and income and you will receive a slip indicating how much you should pay. You can pay at your local convenience store or through online banking.