A black company is basically a highly exploitative company. They will wring out employees for as much as possible, mostly within legal constraints, at the detriment of employees and the benefit of themselves. [0] probably explains it better.
Since changing jobs is seen as a huge risk and the culture among individuals is to remain loyal, it allows black companies to take advantage of naïve, mostly young individuals. You see similar things outside Japan, but less stigma on changing jobs makes it easier to get away from these situations.
>Which things?
E.g.: you don't need to be extremely judgmental of individuals ditching a job to still have the benefits of loyal employees being rewarded and having a family feeling within the company. Which would solve most of the problems with bad/malicious companies taking advantage of the situation.
>[...] these are required to keep most of the solely good things.
Which things?