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 body has been invaded by a mass of cedar pollen! Rushing to the scene so that he can eliminate the cedar pollen, White Blood Cell (Neutrophil) runs into Memory Cell. Memory Cell is a Lymphocyte who retains the immune system’s memories. Seeing what’s actually going on, Memory Cell is strangely flustered. “What the heck? This is just like the legend...” What “legend” is Memory Cell talking about?

Let me become a great red blood cell one day... This is the story of Red Blood Cell before she became Red Blood Cell, when she was a young Erythroblast. The Erythroblasts are training hard to become full-fledged Red Blood Cells under the supervision of their teacher, Macrophage. But Erythroblast is directionally-challenged, and she’s always getting lost in the middle of drills. One day, while practicing to evacuate from bacteria, Erythroblast once again loses her way...

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.

Delivering carbon dioxide to the lungs, and bringing oxygen to cells throughout the body... That’s Red Blood Cell’s important task. Though she’s still directionally-challenged and always losing her way, she can’t be a fledgling forever. She’s determined to go through Circulation by herself without any help from the older cells, but in the shadows, White Blood Cell (Neutrophil) watches over her with a worried look on his face.

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 world (body) is engulfed in sweltering heat. Even after triggering sweat, the body can't be cooled down. Abnormal increased vascular flow, soaring fever... That's right, the body is suffering from heat stroke! Taking advantage of the situation, the Bacillus cereus is rampaging to his heart's content. Reeling from the effects of heat stroke, the usually reliable White Blood Cell (Neutrophil) is suddenly unable to perform... Isn't there any way to save the world from further global warming?

"We have detected life-threatening damage!" Hearing of this emergency, White Blood Cell (Neutrophil) rushes to the blast area. But there, he finds no traces of the blood cells he's supposed to protect! Due to massive bleeding, a huge amount of blood cells have already been flung outside the wound. And the bleeding continues... The situation grows more dire every second, but to protect this world and to save her friends, Red Blood Cell continues to deliver oxygen with Li'l Kouhai Red Blood Cell. Their world is on the brink of destruction... What kind of fate lies ahead for the cells?

A mysterious cell wearing a stylish hat appears before the regular cells, who are bored with just the same (cell division) work repeatedly, every day. This mysterious cell lures the regular cells into a mischievous scheme against White Blood Cell and Killer T Cell. The regular cells enjoy working out their everyday, pent-up frustration. But just who exactly is this cell wearing a stylish hat?

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."