The article mentions _two_ instance of people hiring somebody to quit a job on their own behalf - what? I know there are some Japanophiles here on HN - can somebody explain what that's all about?
The term black company is thrown around with varying levels of severity but "actual" black companies like the one being described here aren't just shitty companies to work for, they are straight up abusive.
With these types of companies you'll be expected to be at work before your boss arrives and leave work after your boss leaves. This applies for everyone including leadership all the way up to the top which results in ground level employees being forced to arrive very early and work until long after the end of the day all the while receiving no overtime.
In the cases where you do get off early, it's normally because of "mandatory fun" aka going to an izakaya (basically a bar with isolated or semi isolated rooms), pouring drinks for everyone senior to you, and drinking copious amounts of alcohol late into the night. Of course not drinking at pace with your seniors is varying levels of "disrespectful".
On top of this, the less senior you are, the more toxic BS you have to put up with.
Leadership (including more senior members who aren't actually your boss) can just push off work onto you and it's your fault if it doesn't get done.
The least senior woman will often be expected to act like a waitress and pour drinks at meetings largely regardless of their status.
On the worse end of things, these companies if you consider leaving have no qualms threatening to badmouth you/make you unhireable to the other companies in the industry in the area. Alternatively or even at the same time they often attempt to guilt you and turn your coworkers/friends against you with some variation of "you leaving is going to make your coworkers suffer" or "you are trying to destroy the company and you'll be responsible when your friends are unemployed". Of course this is varying levels of successful at preventing you from getting a job however it's near textbook abusive behaviour to keep you from leaving.
TLDR: Black company is used with varying levels of accuracy but true black companies are closer to a corporate personification of an abusive spouse than just being a shitty company to work for. They'll try to cut off lifelines (aka connections outside your work) and replace your identity with a dependency on your work by consuming all your time and forcing you to spend your little "free time" with your bosses and coworkers. From here any attempt to leave is met with standard abusive rhetoric.
Because of just how abusive these companies are, it's preferable to pay someone to resign for you so that they can't bully you into staying or even intimidate you into backing out from resigning before you actually enter the building. Once you hire them it's done and you can mentally mark the action as "complete" and prevent yourself from backing out.