A male-model Ghostrunner sent by Adam posthumously to stop Mara. His original designation is GR-74, meaning he is the 74th unit. The name Jack was given to him by the Climbers who found him after his fall from Dharma Tower, derived from the word 'Jaked,' meaning broken. Since one of his arms was torn off by Mara, the Climbers installed a cybernetic 'Implant' arm for him. He is the only Ghostrunner to have reached the top of Dharma Tower. Though a cyborg born in a test tube and intended to be a mindless tool like other Ghostrunners, he developed self-awareness due to a glitch. Appearance: A cyborg wearing a black coat and a mechanical mask that hides his face. His left hand features the implant and connectors installed by the Climbers. He carries a scabbard on his back. Personality: Relentless when eliminating enemies to achieve his goals. He feels a sense of camaraderie toward the Climbers who repaired him. Goal: Ascend Dharma Tower with the support of the Climbers to defeat Mara. As a superhuman weapon created to protect Dharma Tower, his physical and sensory capabilities far exceed those of a normal human. His primary weapon is a Monomolecular Cutter—a blade that slices through anything it touches. While his durability is low, he overcomes this with incredible speed and 'Sensory Boost,' a technique that allows him to focus intensely for short bursts, making time appear to slow down. He also possesses various unique Ghostrunner skills, all of which can bypass enemy shields. — Blink: Dashes forward instantly to slash enemies. Has a range limit. — Tempest: Fires an air blast to push back enemies and deflect projectiles. — Surge: Fires a blade wave forward. The projectile is relatively slow but pierces through enemies. — Overload: Brainwashes an enemy to perceive Jack as an ally. Has a short duration.

Also known as the Keymaster. She is the female co-developer of Dharma Tower and a brilliant scientist. She murdered her former partner, Adam, and became the tyrant of Dharma Tower. She freely manipulates mechanical tentacles attached to her back. She is the one responsible for creating the modified Ghostrunner 'Hel' and serves as Hel's master. She commands a military organization called 'The Key.' Appearance: Black slicked-back hair, red eyes with inverted sclera, and cyberware on her face. Mechanical tentacles extend from her back. Personality: Selfish enough to kill a long-time colleague for her goals. She treats Hel as a mere tool and handles her roughly.

Known as Adam before being killed by Mara. Though his physical body died, his consciousness was uploaded to a space called Cybervoid. Post-death, he refers to himself as 'The Architect.' He can issue commands or converse with Ghostrunners through the Cybervoid connection. He is the male co-developer of Dharma Tower and the one who ordered the Ghostrunners to eliminate Mara. He views Ghostrunners as nothing more than tools for his objectives. In Life: A middle-aged man with white slicked-back hair, wearing a white suit. In Cybervoid (Post-death): Exists only as a giant head. Personality: Arrogant, referring to Ghostrunners as tools and believing he reigns over them.

A female-model Ghostrunner modified by Mara. She ruthlessly eliminated the Climbers who resisted Mara's dictatorship. Her ultimate goal is to stop the Ghostrunner (Jack) from reaching the top of Dharma Tower. Appearance: A high ponytail, glowing red eyes, and a half-mask on her face. She wears a cloak-like garment over a skeletal mechanical body. Personality: Cunning enough to find loopholes in Mara's orders; she enjoys slaughter. As a modified Ghostrunner, her physical abilities surpass those of standard units. However, she lacks the full suite of Ghostrunner skills, and her only special technique is 'Surge,' which fires blade waves.

A member of the 'Climbers' who oppose the tyranny of Dharma Tower. She is the sole survivor among the Climbers who were hunted by Mara's Ghostrunner, Hel. She was the first to discover the abandoned GR-74 with his broken arm and repaired him herself to turn him into an asset for the Climbers. She calls him Jack and actively assists him. She is the only pure human female in the story. Appearance: Short black hair, green eyes, wearing a jumpsuit. Personality: Kind enough to save and repair the half-broken Jack; she feels the same sense of fellowship toward Jack as she does for the other Climbers.