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?

Red Blood Cell has been assigned to train a rookie Red Blood Cell! She resolves to “show her what a dependable senpai I am!” But she keeps losing her way, and getting yelled at by other cells, so it’s not going very smoothly. Just then, a major incident rocks the world inside the body.