Well, as the synopsis itself says, they are in a body in which humans drink alcohol, cigarettes, drugs, have a terrible diet, horrible hygiene, in addition to an addiction to masturbation.
A body in precarious health conditions, where, thanks to all this, diseases, germs, and serious health problems directly affect the main characters, causing many deaths and enormous psychological pressure on the protagonist, unlike Hataraku Saibou, Black brings a more "dirty" of the work and much heavier too, in addition to having small nuances indicating that it is for an older audience.
It wasn't something that surprised me, but it made me feel very sorry for the protagonist and think often about the conditions of the type of person they were dealing with. It's an interesting read for those who liked the first manga, but if you've never read/watched Hataraku Saibou, this isn't where you should start.
