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.