Who killed Gi-seok in Mercy for None? Details explored

Mercy for None is a 2025 South Korean action-noir miniseries on Netflix. Adapted from the webtoon Plaza Wars: Mercy for None, the seven-episode show stars So Ji-sub as Nam Gi-jun, a retired gang enforcer who returns to duty to revive his old life in the world of Seoul after the murder of his younger brother, Nam Gi-seok (Lee Jun-hyuk). What begins as a personal quest for clues quickly reveals a greater conspiracy, exposing systemic corruption, power politics, and the irretrievable consequences of vengeance.

Praised for its gritty emotional depth, Mercy for None unfolds at a glacial, controlled pace rather than traditional speed-of-light action. Each 40–50-minute episode is shrouded in unvarnished realism, building emotional weight behind every application of violence. Nam Gi-jun's character arc is defined by loss, self-restraint, and increasing ferocity. After years of trying to escape the life of a gangster, he is pulled back in by the discovery of dead Gi-seok—a move that triggers a disastrous domino effect on Seoul's underworld.

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Who killed Gi-seok in Mercy for None?

Initially the suspicion falls on Gu Jun-mo, arrogant son of Bongsan gang boss Gu Bong-san. This is due to the fact that he engages in a public altercation with Gi-seok in the run-up to the murder. But this would-be rivalry is a red herring. As Gi-jun digs deeper, he learns of a much broader conspiracy. The mastermind is Lee Geum-son, a prosecutor and son of archrival Juwoon gang leader Lee Ju-woon.

Along with Cha Yeong-do, a crooked senior police officer, Geum-son manipulates Gi-seok's murder to provoke war between the Bongsan and Juwoon gangs. They intend to destroy the existing gang structure and seize control of the criminal and legal machinery in the chaos that follows. The pervading theme of the show—that the most powerful enemies are often in power—is investigated via these characters' manipulation of both the law and the streets.

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The assassin in Mercy for None: A hired hand in the shadows

As Cha Yeong-do and Lee Geum-son orchestrate the murder, Gi-seok is murdered by a hitman, Kaneyama. This character is shown as an emotionless, professional killer. This killer makes an appearance during the second half of the series and is the very embodiment of the clinical detachment of the noir hitman.

While the program does not dwell on the killer's history, his character is pivotal to Gi-jun's unmasking of the conspiracy. The hitman is the embodiment of the mechanical cruelty of power, brutality without responsibility or ethics. His characterization in the series is consistent with noir conventions and resonates with such characters found in K-dramas as Stranger and Beyond Evil.

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Gi-jun's revenge and the fall of Seoul's underworld

As Gi-jun uncovers the conspiracy, his path is one of vicious revenge. He kills Gu Jun-mo, the assassin who killed his brother, and finally confronts Cha Yeong-do and Lee Geum-son. In a climactic conclusion, Gi-jun prevents Geum-son from taking her own life, insisting that he exact his own form of justice.

This autumn of revenge does more than avenge Gi-seok; it destabilizes the entire underworld. The gang war between Bongsan and Juwoon descends into anarchy. Lee Ju-woon and Gu Bong-san are slain in the gang war, while Cha Yeong-do becomes a fleeting authority before being unmasked and destroyed.

Gi-jun uses illegally taped confessionals to reveal the depth of corruption, which provokes public outrage and institutional collapse. This part of the show highlights the main message of the show: justice, when filtered through vengeance, comes to touch everybody.

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The final scene: A barren death in the mountains

In the final episode, Gi-jun limps off into a remote mountain hut—a place he fantasized about running away to with his brother. Mortally wounded, emotionally shattered, and completely alone, he rests beside a campfire as the screen fades to black.

This episode brings the show to a dark but fitting end. It ends Gi-jun's story not in triumph, but in muted devastation, true to the noir fiction's fatalistic tempo.

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Therefore, who killed Gi-seok in Mercy for None? The act was committed by an assassin, but the brains behind the operation were the authorities: a prosecutor and a police officer who used murder as a stepping stone to power.

Mercy for None is a work of fiction, but its motifs—abuse of power, the illusion of justice, and the cost of vengeance—are all too real to the world today. Although it belongs to a growing genre of noir K-dramas, it differs in its emotional core, realistic acting, and bleak conclusion.

Also read: Will there be a Mercy for None Season 2? Possibilities explored