Ernesto Makimura is a foundational character in the City Hunter narrative, though his presence is felt most strongly after his death. He is the original partner of the protagonist Ryo Saeba and the older brother of Kaori Makimura. The name Ernesto is used in some Spanish-language localizations of the series for the character originally named Hideyuki Makimura.

In terms of background, Ernesto Makimura came from a family with a strong sense of civic duty, as his father was a police officer. He followed in those footsteps to become a detective himself. However, his strong sense of justice led him to become disillusioned with the limitations of the legal system, which he felt allowed too many criminals to escape punishment. This frustration drove him to leave the police force after he discovered the identity of Ryo Saeba, the underground sweeper known as City Hunter. Instead of arresting Ryo, Ernesto proposed they form an alliance, believing they could together fight the crime that the law could not touch. Their partnership became highly effective and feared throughout the Tokyo underworld.

Ernesto's personality is defined by a deep commitment to justice and a sense of duty towards his loved ones. As a former officer, he is principled and dedicated to eradicating evil. He is also courageous and loyal, willing to leave a legitimate career to work in the shadows for what he believes is right. His relationship with his younger sister, Kaori, is a central aspect of his character; he cares for her deeply and serves as her guardian. He also harbors romantic feelings for a police colleague named Saeko Nogami, a detective who often worked with him and Ryo. Their relationship has a practical dimension, as Ernesto would provide Saeko with off-the-books assistance through his new line of work.

Ernesto's primary role in the story is as a catalyst. He is the tragic figure whose death sets the entire series in motion. While investigating a powerful drug trafficking syndicate, he and Ryo were confronted and given an ultimatum to join them. After refusing, Ernesto was mortally wounded in a shootout. In his final moments, dying in Ryo's arms, he made two crucial requests: that Ryo protect and take care of his sister Kaori, and that he deliver an engagement ring and the truth about her family to her. This promise binds Ryo to Kaori, who becomes his new partner, creating the central dynamic of the series. His death also serves as a powerful motivator for Ryo, who then single-handedly hunts down and destroys the entire gang responsible for his partner's murder, as an act of vengeance and to fulfill his promise.

Regarding his development, because Ernesto dies so early in the timeline, he does not have an arc within the main story. Instead, his significance is continuously developed through flashbacks, the motivation he provides for other characters, and the legacy he leaves behind. The very foundation of Ryo and Kaori's partnership, and the unspoken romantic tension between them, is built upon the promise Ryo made to the dying Ernesto.

In terms of notable abilities, Ernesto was a competent fighter, but he was known for being particularly skilled with knives, a talent he would often downplay or deny. While his gunfighting prowess was overshadowed by Ryo's legendary skills, his proficiency with bladed weapons made him a formidable partner. His true strength, however, lay not in his combat ability but in his conviction and his strategic partnership with Ryo, which proved to be a lethal combination against crime.