Takasugi is a police lieutenant and detective who frequently encounters the unlicensed surgeon Black Jack. Initially driven by a personal trauma where an unlicensed doctor harmed his son, he strictly enforces regulations and persistently pursues Black Jack's arrest. His protective nature towards friends and family informs this sense of duty. Beyond being an antagonist, he collaborates with Black Jack in the OVA episode "Clinical Chart 2: A Funeral, The Procession Game" to investigate a drug syndicate cultivating mescaline-producing cacti on Mt. Senin. During this case, syndicate operatives abduct them and leave them with a time bomb, forcing them to escape together.

A shift occurs when Black Jack successfully cures Takasugi's son of Pagan disease. This transforms Takasugi from an adversary to a supporter. His later threats against Black Jack become playful and empty, reflecting newfound camaraderie. By "Black Jack 21," he openly regards Black Jack as a friend. Throughout the 1993 OVA series, Takasugi provides recurring comic relief, often appearing with Pinoko to lighten the narrative. His persistence in questioning Black Jack's legitimacy, juxtaposed with cooperation, adds complexity. His character develops from rigid law enforcement to a more nuanced understanding of justice, acknowledging Black Jack's medical ethics despite unconventional methods.