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.

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?