Inside the human body, roughly 37.2 trillion cells work energetically 24 hours a day and 365 days a year. Fresh out of training, the cheerful and somewhat airheaded Sekkekkyuu AE3803 is ready to take on the ever-so-important task of transporting oxygen. As usual, Hakkekkyuu U-1146 is hard at work patrolling and eliminating foreign bacteria seeking to make the body their new lair. Elsewhere, little platelets are lining up for a new construction project.

The cells of the human body never rest for too long; there's always something new to do and learn every day. At least, that's what Hakkekkyuu U-1146 feels as he rushes to and fro, searching for any pathogens that could cause harm to the body. Despite his dangerous line of work, it's all worth it to protect the happy smiles of Sekkekkyuu AE3803, the platelet crew, his fellow neutrophils, and the other cells he meets along the way.