Japan did not have a legally binding working hour limit until 2019, meaning it was perfectly legal for a company to force workers to work 24 hours, 365 days per year. Now, no employer can make its employees work more than 100 hours of overtime per month, which is still 20 hours more than the "karoshi threshold."

The word karoshi （過労死）literally means death from overwork. The leading medical causes of karoshi deaths are brain and heart diseases. The term, first introduced in the 1980s, was coined by a group of lawyers and doctors helping families who lost their loved ones to overwork. Karoshi occurs when an employee works extremely long hours under demanding conditions. The current government threshold for recognizing deaths as work-related is 80 hours of overtime per month ("karoshi threshold").

In 2018, the government recognized 86 deaths as work-related, but labor organizations claim this is just a tip of the iceberg as most families do not even apply to receive compensation, meaning most go unreported.

Karo-jisatsu refers to cases workers commit suicide after experiencing depression from working extremely long hours under mentally demanding conditions. Whereas victims of karoshi are mainly male workers in their 40's or 50's, karo-jisatsu is prevalent among young workers regardless of gender. In 2018, 76 suicides were recognized as work-related by the government. The number of workers suffering from overwork is increasing every year due to the emergence of "black companies," which treats workers as disposable.