Traumatized by ten years of horrific scientific experimentation within Hermes Lab's subterranean facilities, Kim Ji-Oh originally earned the designation "The Skeleton." Following his brutal escape, his core motivation shifts from passive survival and hiding in civil society to an active campaign of vengeance. Despite his cold combat disposition, Ji-Oh retains deep empathy for fellow victims and protects those who show him genuine humanity. Combat abilities and traits: Wielder of the "Heart of Resurrection." He possesses absolute immortal regeneration, allowing him to recover instantly from fatal wounds, decapitation, and organ destruction. By absorbing foreign blood, he amplifies his physical strength, speed, and endurance, evolving biologically during combat.

A empathetic high school student who discovers Kim Ji-Oh following his laboratory escape. Unaware at first of the full extent of the mutant underworld, Hye-Ji offers Ji-Oh shelter, basic necessities, and warm human affection. Her unyielding kindness serves as Ji-Oh's primary emotional anchor, motivating him to preserve his humanity despite his violent nature. Combat abilities and traits: Non-combatant civilian; possesses high emotional intelligence and moral resilience.

The tactical leader of the Mutant Special Police Task Force and older sister to Song Hye-Ji. Pragmatic, highly skilled, and fiercely protective of her family, Hye-In walks a fine line between enforcing government law and waging an unsanctioned war against Hermes Lab. She recognizes Ji-Oh's potential and forms a secret operational alliance with him to dismantle the illegal syndicate. Combat abilities and traits: Advanced combat leadership, tactical intelligence, and force-manipulation abilities capable of suppressing mutant threats in direct engagements.

Formerly known as Subject 0442 within Hermes Lab, Kang Do-Hyung rose to become the President of Hodan Construction, serving as an intermediary for underground dealings. Initially opposing Ji-Oh to defend his corporate empire, Do-Hyung is humbled by Ji-Oh's regenerative power and strong sense of justice. Driven by a desire to free fellow test subjects, he turns his resources against Hermes Lab. Combat abilities and traits: Possesses the "Heart of Rock," granting him geokinetic manipulation, extreme physical durability, stone armor generation, and overwhelming impact power.

A high-risk mutant subject imprisoned and tortured within Han Ki-cheol's hidden research facility. Severe trauma made her cautious of others, but she develops a deep attachment to Kim Ji-Oh after he rescues her from captivity. She stands as a living testament to the atrocities committed by Hermes Lab. Combat abilities and traits: Manifests sharp, organic thorn-like defensive appendages capable of shredding threats and creating defensive barriers.

A former lab survivor turned underground broker. Lee Chae-Won's loyalty was forcibly bought by Hermes Lab after they took his disabled sister hostage. Though burdened by guilt, Chae-Won traps and betrays fellow mutants to guarantee his sister's safety, bringing him into direct conflict with Kim Ji-Oh. Combat abilities and traits: Sword-manifesting Heart Mutant; can sprout sharp metallic blades directly from his limbs for rapid, lethal close-quarters combat.

A sadist and senior researcher for Hermes Lab who oversees secret facility operations and high-risk subject experiments. Ki-Cheol views mutants purely as disposable biological material to be analyzed and broken. His cruelty makes him one of Ji-Oh's primary targets during the facility raid. Combat abilities and traits: Manipulates bio-mechanical construct chains capable of binding, piercing, and restraining high-tier mutant subjects.

The ruthless Executive Director of Hermes Lab. Operating from the shadows, Ju Jin-Hyeok influences political figures and corporate executives to fund his biological research. He views Ji-Oh's "Heart of Resurrection" as both an annoying threat and the ultimate biological prize, ordering his immediate termination and recovery. Combat abilities and traits: Supreme administrative authority over Hermes Lab's military and scientific assets; access to top-tier experimental technology and high-ranking political connections.