Bacteria appear near the stomach. White Blood Cell (Neutrophil) is on the scene at once. There, he finds Eosinophil, another type of White Blood Cell, already in battle, but she’s struggling badly. Seeing how powerless she is, the other cells start trashing Eosinophil behind her back. Even after White Blood Cell (Neutrophil) tells them, “There’s a job that only Eosinophil can do...”

The enemy disguising himself as a common cell has revealed his true identity. He is Cancer Cell. To protect this world, White Blood Cell (Neutrophil), Killer T Cell, and NK Cell must now confront the attacking Cancer Cell in battle.

In the middle of a drill, Killer T Cell tosses a subordinate right into Helper T Cell’s office. The two polar opposites start arguing. According to Dendritic Cell, although they play very different roles today, they were actually classmates at Thymus School. Not only that, but they were totally different back then! What was it that developed between these two during their days of enduring hellish training sessions at Thymus School where only two to three percent of cells manage to survive?

The antibody information of a cell has leaked. There is tension in the air after NK Cell makes a comment to White Blood Cell (Neutrophil). The journey to reunite the lactic acid bacteria with their friends takes the group to the large intestine. In the intestine, which has been irritated due to toxic gas being released by harmful bacteria, the group meets up with Memory T Cell who was formerly known as "Killer T Cell."