Episode 21

"Cancer Cell II (Part II)" (がん細胞II（後編)) is the twenty-first and final episode of the Cells at Work! anime.

Synopsis
White Blood Cell and his comrades confront Cancer Cell, but Regulatory T Cell obstructs their fight. After risking his life to save lactic acid bacteria, Normal Cell finds himself in the clutches of harmful bacteria.

Plot
In the intestines, a group of harmful bacteria are figuring out how to torment Normal Cell when the Neutrophil Division arrive to fight the bacteria off. However, the opportunistic bacteria side with the harmful bacteria as they were impressed with them being the strongest. The tide turns with the arrival of the giant Lactic Acid Bacteria; despite not having much intelligence, their sheer size and nature to help the body allows the immune cells to overwhelm the harmful bacteria, while the opportunistic bacteria immediately side with the immune cells in the process. With the harmful bacteria kept in check, the intestines begin producing normal gas, allowing the rest of the body to breathe easier.

Elsewhere, Cancer Cell torments Killer T and Natural Killer Cell while U-1146 looks on helplessly. Cancer Cell admits that he sees U-1146 in him in that they don't like their preordained destinies and continues seeing him as a friend, while he loathes the other two for killing his kind without remorse. As Regulatory T Cell is still insistent on protecting him, Cancer Cell begins to siphon power from the toxic mass.

Killer T refuses to give up, stating that he still has one more move up his sleeve; the Perforin Cannon Punch, although no one takes him seriously. He had learned of it while training, although the Killer cells that told him about it had simply made it up. Despite this, he was insistent on practicing the move and is eventually able to perform the move. Regulatory Cell dodges the attack, causing Cancer Cell to be struck by it. The move allowed her to realize that Cancer Cell is a threat to the body and that she had realized it when she noticed that his shirt read "CLL" instead of "Cell", much to Natural Killer and Killer T's astonishment.

Cancer Cell creates a large tumor to attack the trio; while impervious at first, the cells are able to destroy it and attack him. Cancer Cell boasts that they can't harm him, but his wings crack and he falls to the ground, demanding an explanation as to what's happening. U-1146 explains that the intestinal tract is returning to normal, killing off the toxic mass in the process that he was siphoning power from. Cancer Cell then realizes that U-1146 has broken out of the containment tube and realizes too late that the Neutrophil is right behind him, who mortally wounds him. Cancer Cell concedes and dies again, content that U-1146 was the one who finished him off and not the other cells.

Back above, the Neutrophils no longer sense any harmful bacteria as the lactic bacteria go to work in repairing the damage. U-1146 thanks Normal Cell for saving the body, as him saving the small lactic bacteria and bringing them back to their friends allowed them to turn the tide. The black lactic bacteria brings the pair into the intestinal flora so the cells can see their world, consisting of all types of bacteria that astonishes them. After returning to their surface, Normal Cell bids farewell to the lactic acid bacteria.

As the body resumes its daily routine, AE3803 informs U-1146 during a meal break that Normal Cell is homeless as the Platelet Division did not repair his unit due to him not being present. The two decide to help him out whenever they have the chance as AE3803 resumes her duties. At the T Cell camp, Killer T tries to teach the Perforin Cannon Punch to a group of Naive T Cells, although he fails to perform the move. AE3803 soon brings her package of oxygen to her recipient.

Returning characters

 * Normal Cell
 * Lactic Acid Bacteria
 * Platelet Division
 * AE3803
 * Killer T Cell
 * Natural Killer Cell
 * U-1146
 * Cancer Cell
 * Regulatory T Cell
 * Intestinal epithelial cells
 * Goblet Cell