The entire premise. If you drink, smoke, have unprotected sex, eat unhealthily, or just plain overwork without rest, your body will eventually give up, refuse to work and will almost die of heart attack.
The way bacteria are depicted here. Unlike in the main series, where they act as typical shounen antagonists, here they are monstrous Humanoid Abominations who show no mercy and kill everything in sight. Compare the pneumococcus of the main series (who was your standard Card-Carrying Villain) to the ones in the first chapter, who look more rugged, only emit growls and don't even try to communicate with the red blood cells, just killing them. The gonococcus of chapter 4 are even worse, looking like huge phalic monsters from some tentacle porn hentai who leave lots of pus (i.e. neutrophil corpses) around the body. It doesn't help that they have some rape vibes in the way they fight and kill neutrophils, nor that they have tentacles that not only also have form of penises, but they have eyes and mouths too.
A bit of Ascended Fridge Horror...remember how fans have wondered what autoimmunity would look like in a setting of cells as people? Here we get to see... and it's the Killer T Cells, so overworked from the harsh conditions of the body that they've gone insane and started to murder the body cells themselves, thinking them to be enemies.
Their appearance in the chapter only makes it even more horrific. The T Cells are brutally beating up the hapless Hair Follicle Cells, with their bare fists, or hammers twice as big as the Killer T's are, and while they look like berserk animals, you can't help but feel that they're also terrified, fighting for their lives and the host body's, being constantly whipped and kept in this state of frenzy by the well-meaning Commander T Cell continuously releasing cytokines.
The effects that carbon monoxide from smoking have on Red Blood Cells. It makes them insane, turns their eyes blank and makes their veins visible from their bodies. It also leaves them vulnerable to the attack of the ferocious bacteria mentioned above.
What's even worse, this is the result of the body relapsing after not smoking for ten years. The Cilia Cells were just getting it clean enough to semi-function at normal levels again when it happened.
Gout: giant, crystalline structures that completely destroy huge swathes of cellular districts, that the Macrophages and Neutrophils can't even make a dent in, and this is after they pull out the bazookas and the assault rifles.
The Hepatocyte in Chapter 6 appears weak, disheveled and with bags under her eyes from being overworked. Given that she's in that state because of the body's owner's excessive alcohol consumption, it's impossible not to draw some unsettling parallels.
When the Red Blood Cells are tasked with transporting too much glucose, they become glycated. This is depicted by them burning alive. This happens multiple times in the later chapters.
After the body starts recovering from depression and making efforts to quit smoking, we are treated to some of the other cells making progress in their lives in the tailend of chapter 36. K-9999, one of the Lung Cells involved during the pulmonary embolism chapter, is fit to start interviewing for work at the lungs... but when he's rejected, he starts succumbing to despair and showing deformities. Those familiar with the mainline manga will recognize the deformities as being from Cancer Cell.
Following from the above, K-9999 follows a mysterious voice to a collection of cells, all with his resemblance, and every single one of them morphing into cancer, beckoning him to join the bunch of rejects.
Cancer Cell's metastasis is depicted as numerous copies of his twisted form manifesting all across the body from every nook and cranny. The body's means of combating it is through radiotherapy and chemotherapy. The former is depicted as a laser beam that fries Cancer Cell from above. The latter is a carpet-bombing with drugs, and the regular cells aren't exempt from its effects.
Compared to regular Cells At Work, who consider the body an impersonal "world" and don't generally question why disasters keep befalling it, the cells in CAWB seem to be more aware of the body as controlled by some entity that's providing them with such a hostile work environment. They somehow know most erections and ejaculations are non-procreative, they're aware that the poor diet and intake of smoke and alcohol are probably an attempt to cope with stress, during the gout breakdown Red Blood Cell furiously insists that the body will hear the cells screaming if they hurt it, a stomach cell yells "Scumbag! Chew your food properly!", they interpret tears as signs of remorse... This is disturbing in either direction. To the cells it's either God Is Evil or in a general sense of helplessness (most likely the latter in terms of the body in question throughout the story). From the human side, it's bad enough to be under constant stress, turning to addictive substances and risky behavior to make things bearable, and medicating heavily for an endless list of health problems without that harming other people, who're aware and critical of your every action.
