@mutei
Enough that they have a word meaning specifically "death by overwork" ("karoshi").
Reports of people working more than 35 hours in a row without pause or sleep, 100 hours a week or 3000 hours a year.
Mostly ending in suicide or heart-attacks at ages less than 40 yo.
Not all japanese companies are like that, but it is happening often enough that manga artists considers an employee from a "black company" the kind of character that people can identify with.