Episode 6

Plot
AE3803 is working when she arrives at her homeland, the Red Blood Marrow. She sees several Erythroblast and a Macrophage, who graduates the Erythroblast valedictorian. She recalls her time as an Erythroblast when she was a Precursor cell, and was made an Erythroblast because she had red hair.

Macrophage teaches them how to become red blood cells. One of the lessons is to deliver oxygen from one side of the room to the other, as they are expected to do so as red blood cells. AE3803 is confused and gets lost, smashing through a wall and begins to cry. Macrophage reassures her.

In the second lesson, Macrophage explains to them that the blood vessels are not always peaceful, as bacteria show up from time to time. She brings in a Neutrophil to cosplay as a Pseudomonas bacterium. The Erythroblasts are to run away from the bacterium by hiding in a corner. AE3803 asks the Neutrophil if she will get lost again, but Macrophage explains that because they are young, they cannot leave the bone marrow until they mature; if they do get lost, they will be able to find them. As the lesson starts, the Neutrophil chases the Erythroblasts around; Macrophage then realizes that AE3803 is missing.

AE3803 ran too far and has hidden herself in a more secluded area and wonders if she can even become a red blood cell. A tentacle grapples herm which AE3803 initially mistakes for as the Neutrophil associate, but is instead a genuine Pseudomonas. AE3803 runs away, but she runs into a door leading to the blood vessel; as an Erythroblast, she cannot leave. She throws her hat at the Pseudomonas, enraging it. The bacterium catches up to her and tries to finish her off, but a young Myelocyte arrives to protect her.

The Pseudomonas easily overwhelms the Myelocyte, as he is inexperienced and fighting with a plastic weapon. The bacterium tells the Myelocyte that it will spare him if he hands over the Erythroblast, but he refuses. Just as the Pseudomonas prepares to fight again, the Neutrophil associate comes in and kills it. Macrophage and Neutrophil comfort their students and bring them back to their respective marrows; but before they do so, AE3803 and the Myelocyte promise to meet each other again.

Back in the present, AE3803 reminisces and resumes her job when she drives the cart over a Neutrophil's foot, who is shown to be U-1146. She gives him a new cup of tea and he assumes that she is lost again, which she confirms. He agrees to take her to where she needs to go. AE3803, recalling the memory, wonders if the Myelocyte that protected her was actually U-1146, but decides against it because it would be too much of a coincidence.

AE3803 thanks U-1146 for bringing her to her destination. U-1146 comments on how peaceful the world is and hopes that it could stay that way. However, he then hears screaming; a warped normal cell is on the rampage. U-1146 kills the cell; Killer T Cell soon greets him, while an unknown cell watches from above. The two talk about how no jobs have come in recently, and as Killer T begins to confiscate the corpse, the unknown cell makes its move and lands on him. U-1146 realizes that the cell is Natural Killer Cell.

Natural Killer examines the corpse and realizes that it is a cancer cell. She asks the normal cell (who was trying to interrupt the conversation between U-1146 and Killer T) where the rest of the cancer cells are hiding. Killer T demands to know where the cells are, but Natural Killer states that she is doing the job alone. Killer T and Natural Killer begin fighting each other in a series of "accidents". U-1146 tells the normal cell that he doesn't need to accompany them as they will be killing his friends. The cell thanks him for being rescued, as it is his first time.

They arrive at the apartment where the cancer cells are hiding. The three immune cells note that the place is deserted and U-1146 decides that they should report to headquarters before moving together. However, Killer T refuses to work with Natural Killer, so she takes the normal cell with her while U-1146 and Killer T go another way.

Now alone, Natural Killer confronts the normal cell, knowing that he is a cancer cell. Cancer Cell drops his innocent facade and prepares to fight her.

New characters

 * Hemopoietic Stem Cell (flashback)
 * U-1110 (flashback)
 * OT0109 (flashback)
 * Natural Killer Cell
 * Cancer Cell

Returning characters

 * AE3803
 * Macrophage (flashback)
 * AA5100 (flashback)
 * Pseudomonas (flashback)
 * U-1146
 * Killer T Cell

Differences from the Manga

 * Half of this episode contained chapter 8 as well as 7.
 * When backhanding Killer T cell in the manga, NK cell wasn't holding her saber.