Keiichi Ikari is a central figure in the psychological thriller anime Paranoia Agent. He serves as one of two police detectives assigned to investigate a series of bizarre and seemingly random street assaults committed by a juvenile delinquent known as Shonen Bat, or Lil Slugger. Ikari is a middle-aged man, likely in his forties or fifties, with a slightly overweight build, a receding hairline, and a thin mustache and goatee. His typical attire consists of a button-up undershirt, an open buttoned coat, black dress pants, and a red belt. He is a veteran officer who originally joined the police force with the nostalgic dream of chasing old-fashioned thieves who wore bandannas and carried large burlap sacks. This idealistic beginning stands in stark contrast to the modern, more complex criminal cases he now faces, leaving him feeling like an old piece of a puzzle that no longer fits.

Personality-wise, Ikari is characterized by his hot temper, skepticism, and old-fashioned sensibilities. He is quick to anger, especially when dealing with disrespectful suspects or what he perceives as foolishness, and he approaches the Shonen Bat case with a strong desire for the most logical and grounded explanation. Initially, he is convinced the attacks are a hoax, a viewpoint that puts him at odds with his younger, more open-minded and optimistic partner, Mitsuhiro Maniwa. Despite his gruff exterior, his motivations are deeply personal and grounded in a sense of duty and love. He continues to work hard primarily to support his wife, Misae Ikari, who suffers from a debilitating heart condition. The stress of the investigation becomes so intense that it causes him to relapse into smoking, even switching to an older brand of matches that reflects his desire to remain in the past.

Ikari's role in the story extends beyond that of a simple investigator. He represents the struggle to confront harsh reality rather than escape from it. As the mass hysteria surrounding Shonen Bat grows, and the comforting but delusional fantasy world of the mascot character Maromi begins to envelop the city, Ikari becomes trapped in his own ideal fantasy. In this personal paradise, he is a celebrated hero, partnered with the first victim, Tsukiko Sagi, who is imagined as his daughter in a world that resembles a simpler, more heroic era of policing. His development hinges on breaking free from this delusion. The catalyst for this awakening is the death of his wife, Misae. Her strength and unwavering love, demonstrated when she faced down Shonen Bat herself without fear and urged him to be strong, provide Ikari with the resolve to abandon his fantasy and return to reality. This act of resistance positions him and his wife as the closest thing the story has to heroes, as his ability to reject delusion ultimately helps inspire the same in others.

Notable abilities of Keiichi Ikari are not physical or supernatural, but rather psychological. His greatest strength is his innate resistance to delusion and fantasy. While many characters, including his partner Maniwa, are either consumed by or seduced by the escapism offered by Maromi's world or the panic of Shonen Bat, Ikari demonstrates a unique capacity to break down his own ideal fantasy and confront an unpleasant reality. This strength, forged by his grounded sense of duty and the memory of his wife's courage, makes him a pivotal figure in the narrative's resolution. His key relationships are primarily with his partner Maniwa, whose idealism clashes with his own realism, and with his wife Misae, whose silent strength is the bedrock of his own convictions.