Red Blood Cells are summoned to handle an emergency. They carry as much oxygen as they can to the scene, but they discover that the stomach has an ulcer and is badly breached. If the serosa becomes perforated, the stomach will end up melting down. Due to the excessive secretion of gastric acid, the body may die at any moment, but the Red Blood Cells continue to desperately carry oxygen. However, the gastric mucosa is being eaten away, and inflammation is getting worse. In such a disastrous situation, a dangerous enemy appears.

Still unable to find meaning in his work, Red Blood Cell (AA2153) is determined to continue delivering oxygen and works hard at his job. Contrary to his determination, the body’s internal environment continues to decline. Plaque, which is made up of cholesterol and fat deposits, has accumulated on the inner walls of the blood vessels, causing them to deteriorate. The buildup of plaque has even affected the coronary arteries which wrap around the heart and supply oxygen and nutrients to the entire heart muscle…

Red Blood Cell (AA2153) repeatedly sees flashbacks of his fellow Red Blood Cell (AC1677) falling into a sea of gastric acid and beats himself up for not being able to save his friend. However, this body does not have the wherewithal to let Red Blood Cell recover. While lack of sleep and exercise is pushing the body into a state of disarray, a sharp and huge inanimate object is found floating midair. An attack from a mysterious germ begins…

Inside the human body, the Red Blood Cells that were produced after erythroblast enucleation, watch an orientation video explaining that they will be going to a fun work environment, but they find themselves at the mercy of their seniors who make unreasonable demands to them without explaining anything about the job. Red Blood Cell (AA2153) carries oxygen all over the body while still in a state of bewilderment, and is shocked to find that the cells he saw in the orientation video are now overworked and look like a mess…

The Red Blood Cells have been given an important mission to fill the erectile tissue with blood to trigger an erection. Red Blood Cell (AA2153) is enthusiastic about the opportunity to contribute to the birth of new life. However, after overcoming various struggles, the exhausted cells must face their arch enemy, the gonococcal cells, known for multiplying at astonishing rates. Though they are vastly outnumbered, the White Blood Cells (Neutrophils) fight the gonococci with everything they have. The desperate battle to protect this body and their world begins now…

There are no such things as rookies in this workplace. Even on the first day of the job, Red Blood Cell (AA2153) and his coworkers have to carry oxygen throughout the body without rest. Red Blood Cell (AA2153) sits down after an exhausting day of work when a veteran Red Blood Cell appears in front of him. “This is just my hunch as a veteran… but on a day like this, it’s going to pour.” Red Blood Cell (AA2153) has no idea what the veteran means by this, but immediately afterwards, they find themselves caught in a shower of alcohol. The Red Blood Cells make their way to the liver to relieve their stress from work…

Red Blood Cell (AA2153) has gained confidence in his work after overcoming numerous obstacles. Along with White Blood Cell, he vows to create a better world and is overcome with a sense of purpose in his work, but shortly after, inflammation is found in the hair follicles. Red Blood Cell discovers that the Killer T Cells, who are normally reliable colleagues, are attacking Hair Matrix Cells and destroying the follicles.

Bodily functions are coming to a halt. In this dire situation, all the cells are on the verge of losing hope, but only Red Blood Cell (AA2153) hasn't given up. Are they making us work hard because the body is unhealthy? Do we stop working because the body is going to die? After experiencing various diseases and losing his friend, the answer that Red Blood Cell (AA2153) and the other cells find is...

An accident occurs where the oxygen delivered by Red Blood Cell (AC1677) to a young Ordinary Cell transforms into reactive oxygen, causing the Ordinary Cell to age. Though it was an accident, he is overcome by guilt for making a cell grow old. Shortly after, an awards ceremony is held for new Red Blood Cells, where AA2153 is chosen for the Rookie of the Year award. Though they started on the job at the same time, AC1677 is pained by a sense of inferiority towards his coworker, but a senior Red Blood Cell approaches him and says that he understands how he must feel. The senior Red Blood Cell says, “I know a place that will make you feel better,” and tries to take AC1677 somewhere.

Due to an increase in smoking and alcohol consumption, the liver has lost the vitality and vigor it once had. It is apparent that the Liver Cells are unhealthy, and according to these cells, too much fat has built up in the liver which has caused the functions of this organ to deteriorate. While Red Blood Cell (AA2153) is bewildered by this situation, he is asked by other Red Blood Cells to help carry oxygen because they are lacking in numbers. The Red Blood Cells are unable to get any rest, but the calves are in a weakened state, so they decide to deliver oxygen to a deep vein that is oxygen deprived…

White Blood Cells are nowhere to be seen, and White Blood Cell (1196) is alarmed by this abnormal situation. Red Blood Cell (AA2153) is worried about the deteriorating health of the body but continues to deliver oxygen. He happens to see newly recruited Red Blood Cells undergoing training. Since Red Blood Cell (AA2153) has been recognized for his recent achievements, he is chosen to train the new recruits and is asked to deliver oxygen with them. However, Red Blood Cell (AA2153) pushes himself too hard without rest while trying to set a good example for the new recruits, and…

Gonococci have entered the body through sexual intercourse. The White Blood Cells are forced to fight an uphill battle with the gonococci, who are known for their unbelievable proliferation rate. The gonococci have invaded the areas surrounding the urethra and are closing in on the epididymis where the sperm are. In order to stop any further advancement of the gonococci, White Blood Cells wage an all-out war against them in the lymph node. Meanwhile, Red Blood Cells have been assigned with the dangerous task of delivering oxygen to the urethra.

Red Blood Cells AA2153 and AC1677 are getting accustomed to their jobs and even have enough energy to joke around during their downtime. They head to the kidneys to wash away the dirt accumulated on the job, where they meet the Glomeruli who work silently to filter the blood. A young Glomerulus warns Red Blood Cell to be careful when getting close to the ureter. When the Red Blood Cells arrive at the efferent arteriole, they hear the ominous sound of something blocking the nearby ureter…