Jōji Ogami, also known as Kyoji Ogami, is the primary male lead and the director of Ogami General Hospital. He is a doctor and a scientist of considerable skill, carrying on the family medical legacy as the third Dr. Ogami to run the institution. His outward demeanor is harsh and often cruel, especially towards the main character, Nanako Shichigusa. He is prone to yelling, issuing threats, and even engaging in physical abuse, yet this behavior masks a deeper, more complex role as her reluctant protector.

His personality is defined by a stark contrast between a caustic, tyrannical veneer and a hidden heroic core. Jōji frequently alternates between the archetypes of an evil mad scientist and a knight in shining armor, typically rescuing Nanako from the monsters and catastrophes that plague their lives at the climax of each episode. This dual nature is a central driving force of his character. Beneath his abrasive exterior, he is driven by a profound, long-standing motivation rooted in tragedy. As a young child, he was cared for by Nanako B, the second clone of the original Nanako. When she fell ill and died before reaching the age of twenty from a mysterious genetic illness, the young Jōji was devastated. He made a solemn vow to become a doctor and cure the Nanako illness, a promise that dictates nearly all of his actions.

In the story, Jōji serves as the head of the hospital where Nanako works as a maid, a role that puts him in constant conflict with her clumsy and accident-prone nature. He subjects her to rigorous and often bizarre physical training, which is part of his larger, secret plan to save her life. His role is that of a seemingly merciless taskmaster whose true goal is the preservation of Nanako, the third clone, from the same fate that befell her predecessors. His key relationships are central to the plot. His bond with Nanako is the most significant; while he treats her with constant frustration and anger, he is also the only one who can ultimately save her from danger. He holds a deep, unspoken, and complicated affection for her, driven by his past failure with Nanako B. He also interacts with a small supporting cast, including a former college rival, Alan Mizuki, and mysterious government operatives and scientists involved in outlandish experiments concerning the Pentagon and the Vatican.

Jōji Ogami undergoes considerable development throughout the series. While his current personality appears fixed, his backstory reveals a significant evolution from a kind-hearted boy into a stern and seemingly heartless man, a transformation born from the trauma of watching someone he cared for die. His present-day actions, which often seem cruel, are continually reframed as desperate measures taken in his long quest to break the clone cycle. His development is not a change in character but a gradual revelation of the tragic history and noble intention behind his abusive behavior. In terms of abilities, Jōji is a highly capable and innovative medical doctor and bioengineer, with knowledge ranging from cybernetics to genetics. He is also resourceful and brave, as he consistently confronts and defeats various monsters and military-grade robots. He is a competent field operative, able to pilot aircraft and engage in dangerous rescue missions, relying as much on his intellect and courage as on his scientific expertise to overcome the bizarre threats he faces.