Once Upon a Time... Life combined entertaining storylines with factual information, presented metaphorically.
The series used the same characters from the other Once Upon a Time... seasons: the good characters represent the cells that make up the body's systems and defense mechanisms, such as red blood cells, white blood cells and platelets, while the bad characters represent the viruses and bacteria that threaten to attack the human body. Every episode of the series featured a different organ or system within the human body (like the brain, the heart, the circulatory system, etc.).
The series also makes use of recurring human characters originally from Once Upon a Time... Man. Every character in the series appeared as a real person (the old intelligent doctor, the dedicated blonde mother, the boy and the girl, their obese friend, and the pair of bullies) and anthropomorphic representations of cells and cellular functions within the human body.