One day, while White Blood Cell (Neutrophil) is busy exterminating germs, he meets Backward Cap, a Platelet who wears her cap backwards. She is secretly training to become a stronger Platelet. However, a huge rumbling noise suddenly echoes inside of the body followed by violent shaking.

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."