Keicho Nijimura is a significant antagonist in the story, serving as the older brother of Okuyasu Nijimura. He is an eighteen-year-old young man with a slim build, sharp features, and light-colored eyes with a distinct, ripple-like pattern in their irises. He has blond hair and is often seen wearing a school uniform, which contrasts with the ruthless actions he undertakes.

Keicho's personality is defined by a cold, rational, and merciless demeanor, especially when compared to his more impulsive and less intelligent younger brother, Okuyasu. Keicho openly admits that his ability to think and reason far surpasses that of his brother, whom he often belittles for his lack of strategic thinking. He operates under a harsh, social Darwinist philosophy, believing that people who do not grow or prove their worth do not deserve to live. This ruthless worldview drives him to commit terrible acts without apparent remorse, such as shooting his own brother to get a clear shot at an enemy and dismissing the injury as Okuyasu's fault for being incompetent. He shows no guilt over harming innocent people with the Bow and Arrow, even when the consequences prove fatal or disastrous, as was the case with the serial killer Angelo.

The primary motivation behind Keicho's cruel actions is a desperate and tragic goal. Years before the main events, his father was a man who fell into deep debt and despair after his wife's death. To escape this situation, the father sold his soul to the vampire DIO, who implanted a flesh bud in his head. When DIO was defeated by Jotaro Kujo, the flesh bud caused Keicho's father to slowly mutate into a monstrous, immortal, and mindless creature that could heal from any wound. Traumatized by this transformation, which occurred when he was a child, Keicho dedicated his life to finding a way to end his father's miserable existence. He discovered the Bow and Arrow, an artifact that can forcibly awaken Stands in people. Keicho's role in the story is that of a Stand creator; he systematically shoots people in the town of Morioh, hoping to find someone whose newly awakened power would be strong enough to kill his immortal father.

His key relationship is with his brother, Okuyasu, which is complex and fraught with tension. On the surface, Keicho is harsh and abusive, treating Okuyasu as a tool and showing little patience for his failures. However, buried beneath this cruelty is a deep-seated protectiveness. This is ultimately proven when the electric Stand Red Hot Chili Pepper ambushes them. Keicho pushes Okuyasu out of the way of a fatal attack, taking the lethal blow himself and sacrificing his own life to save his younger brother. In his final moments, he reveals his true desire was not born of malice but from a twisted sense of mercy for his father.

Keicho undergoes a subtle but tragic development. He enters the story as a calculating and seemingly heartless villain, but his death re-contextualizes his actions. His sacrifice demonstrates that his cold exterior masked a genuine, if misguided, love for his family. He appears later as a ghost to encourage a nearly dying Okuyasu to continue living, showing that even in death, he cares for his brother's well-being.

In terms of abilities, Keicho possesses a powerful Stand called Bad Company. This Stand is unique in that it is a colony-type, meaning it is not a single entity but an entire miniature army. Bad Company consists of dozens of tiny soldiers equipped with working rifles and combat knives, several small tanks that fire explosive shells, and attack helicopters armed with missiles and machine guns. Despite their miniature size, the weapons are capable of causing serious injury or death to a normal human, and their coordinated firepower can overwhelm even powerful Stands. Keicho commands this tiny army with meticulous precision, using it to set traps, create walls of suppressive fire, and launch devastating all-out assaults from both ground and air.