"Cells at Work!!" is a science-themed anime that personifies the various cells and microorganisms within the human body, depicting their daily functions as if they were workers in a bustling city. The narrative centers on a red blood cell, AE3803, whose primary role is to deliver oxygen and nutrients throughout the body while collecting carbon dioxide for removal. Despite her earnest efforts, AE3803 is often clumsy and prone to getting lost, leading to frequent encounters with other cells and microorganisms.

One of the key figures in the series is a white blood cell, U-1146, who specializes in combating pathogens such as bacteria and viruses. U-1146 is highly skilled and efficient, often coming to AE3803's rescue when she encounters dangerous situations. Their dynamic forms a core part of the story, with U-1146's protective nature contrasting with AE3803's vulnerability and determination.

The series explores various biological processes and health scenarios through episodic storytelling. Each episode introduces new challenges, such as injuries, infections, or allergic reactions, which the cells must address to maintain the body's health. For example, when a scrape occurs, platelets are depicted as construction workers who quickly form a clot to stop bleeding, while white blood cells fend off invading bacteria. Similarly, during an influenza outbreak, the immune system mobilizes its defenses, with killer T cells and macrophages playing pivotal roles in neutralizing the threat.

Other notable characters include a memory cell who retains information about past infections, a naive T cell who undergoes training to become a killer T cell, and a platelet who is small in stature but crucial for blood clotting. The series also introduces antagonistic entities like cancer cells, which threaten the body's stability and require coordinated efforts from multiple cell types to eliminate.

The narrative balances educational content with action and humor, presenting complex biological concepts in an accessible and engaging manner. By anthropomorphizing cells and microorganisms, the series provides a unique perspective on the inner workings of the human body, making it both informative and entertaining.