What is National Health Insurance?

Japan's health insurance system is a "universal health insurance system" in which everyone is enrolled in some form of medical insurance.
National Health Insurance is a mutual aid system where all members contribute to the National Health Insurance Tax to cover necessary Medical Expenses in preparation for illness or injury.
Those who are enrolled in their workplace health insurance (such as Health Insurance, Seamen's Insurance, Mutual Aid Associations) and their dependents, those enrolled in the Late-Stage Elderly Medical Care system, and those receiving Public Assistance are the only exceptions. All others, regardless of age or occupation, are required to enroll in the National Health Insurance. (For example, self-employed individuals, those engaged in agriculture, part-time workers not enrolled in their workplace health insurance, and those who have retired and left their workplace health insurance.)