In the anime Cells at Work!, the character known as Memory Cell is a male lymphocyte whose primary function is to serve as the immune system's archivist. He is a specialized white blood cell, specifically a B lymphocyte, that does not participate in direct combat. Instead, his role is to record detailed information about every pathogen, antigen, or foreign substance that has ever invaded the body, ensuring that the immune system will be prepared to mount a faster and more effective response if the same threat appears again.

In his appearance in the main series, Memory Cell has an average build with messy black hair and dark eyes. He is typically dressed in a black polo shirt, grey slacks and vest, and a purple tie, giving him the look of a harried office worker or librarian. His personality stands in stark contrast to the aggressive and determined killer T cells. He is often depicted as scatterbrained, anxious, and prone to panic, especially when an invasion occurs. Despite his impressive memory capacity, he has a negative mindset and is constantly overthinking, which makes it difficult for him to perform his duties calmly and efficiently. He tends to record past biological events in an overly dramatic and confusing manner, sometimes describing a common cold or an allergy as if it were a legendary doomsday prophecy. This has led to him being characterized by fans as somewhat of a chuunibyou, or someone with delusions of grandeur, as he interprets his own records as ancient, cryptic legends.

A key relationship is with his fellow lymphocyte, the B Cell. Memory Cell works closely with B Cell, providing the necessary antigen records so that B Cell can produce the correct antibodies to neutralize a recognized threat. His function is the biological basis for acquired immunity and the principle behind vaccines, as the body becomes permanently immune to a virus once Memory Cell has stored the data on how to defeat it. One of his notable abilities is to refer to immunological data passed down through genetics. While this is a crucial defense mechanism, it can also be a liability, as it may lead to an overreaction against harmless invaders like pollen, which manifests in the body as an allergic reaction. His role in the story is largely supportive, often appearing in episodes concerning recurring infections or allergies, where he is seen desperately searching through his records or warning other cells about an impending crisis based on his often-overwrought interpretations of past data.

It is important to distinguish this character from the Memory T Cell, who also appears in the series. While both share the function of storing immunological memory, the Memory T Cell is a subtype of the killer T cell, retains combat abilities, and has a more assertive and studious demeanor, complete with a notebook of enemy move-sets. The standard Memory Cell, by contrast, is a non-combatant B lymphocyte whose struggles are more intellectual than physical. In the spin-off series Cells at Work! BLACK, a different version of the Memory Cell appears, working in a severely unhealthy body. This iteration has short, light-colored hair but retains the same core duty of recording pathogen information to support the immune system.