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. Dealing with wounds and allergies, getting lost on the way to the lungs, and bickering with similar cell types, the daily lives of cells are always hectic as they work together to keep the body healthy! [Written by MAL Rewrite]

Due to poor lifestyle choices, a certain human's body is in constant turmoil. With germs, bacteria, and foreign substances abound, the jobs of various cells become increasingly difficult and dangerous. As some of the unfortunate ones who matured in this chaotic environment, Sekkekkyuu AA2153 and Hakkekkyuu U-1196 strive to fulfill their duties—even if it means seeing many of their fellow cells lose their lives in duty. Set in an environment vastly different from its parent story, Hataraku Saibou Black portrays the cells' struggles as they try to maintain the body's health. However, the human's condition continues to deteriorate, and whether or not these efforts will amount to something concrete depends on the cells! [Written by MAL Rewrite]

Due to poor lifestyle choices, a certain human's body is in constant turmoil. With germs, bacteria, and foreign substances abound, the jobs of various cells become increasingly difficult and dangerous. As some of the unfortunate ones who matured in this chaotic environment, Sekkekkyuu AA2153 and Hakkekkyuu U-1196 strive to fulfill their duties—even if it means seeing many of their fellow cells lose their lives in duty. Set in an environment vastly different from its parent story, Hataraku Saibou Black portrays the cells' struggles as they try to maintain the body's health. However, the human's condition continues to deteriorate, and whether or not these efforts will amount to something concrete depends on the cells! [Written by MAL Rewrite]

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. In his latest pathogen-hunting adventures, Hakkekkyuu U-1146 discovers how important cells can sometimes make mistakes, and that not all bacteria are actually bad. Everybody has their bad days, but everything eventually works out when their comrades have their backs. In the end, it's just another normal day for these hardworking cells! [Written by MAL Rewrite]