Jonah, whose full name is Jonathan Mar, is a central figure in Jormungand Perfect Order. He is a pre-adolescent boy who serves as a bodyguard for the international arms dealer Koko Hekmatyar, though his history is deeply rooted in the violence of the battlefield. His background is tragic; his parents were killed in an airstrike in his war-torn homeland, an event that directly led to his life as a child soldier. This past has forged in him a profound hatred for weapons, which he believes are the root cause of death and destruction. Despite this deep-seated loathing, fate has placed him in the employ of one of the world's most prominent arms dealers, a contradiction that defines his daily existence.

Personality wise, Jonah is predominantly stoic, quiet, and hyper-competent in combat, which is a direct result of his conditioning as a soldier. He rarely shows overt emotion, yet he is not a hollow shell. Deep within, he retains the vulnerability and wants of a normal child. He exhibits genuine happiness over simple pleasures, such as going to the beach or seeing stuffed toys, experiences that were likely denied to him during his early years on the front lines. This hidden innocence is most poignantly displayed when he observes a group of orphans he once saved now living happy, peaceful lives. His face shows undeniable happiness and longing, yet he chooses to remain hidden, refusing to disrupt their normal existence with his own presence. This act reveals that while he may appear to be a mature soldier, he is also a child who understands that he has lost his chance at a normal life.

Jonah's primary motivation shifts and evolves throughout Perfect Order. Initially, he seems to be a mercenary surviving by his skills, held to Koko’s side by circumstance and a debt of gratitude for her help in securing a future for the orphans he cared for. He is a mess of contradictions, despising arms dealers while relying on one for his livelihood. As the series progresses, his motivation moves beyond simple survival and begins to grapple with larger ideologies. He is confronted with the scale of Koko’s ultimate plan, Jormungand, which is designed to forcibly end all air-based warfare. This revelation forces Jonah to face his hatred of weapons and consider whether an extreme act can justify a peaceful end, making his personal journey about finding a place for his skills in a world he wishes to change.

In the story, Jonah serves as the primary observational lens and the emotional core of the team. As Koko’s most trusted bodyguard, he is frequently on the front lines of the squad’s military operations, using his unique talents to protect the group. His role is also symbolic; his presence grounds Koko and the narrative by constantly reminding the audience of the human cost of the arms trade. He is a living example of the chaos that Koko’s clients create, which adds a layer of tense irony to every firefight and deal.

Key relationships heavily influence Jonah’s development. His bond with Koko is the most central. She is his employer, but she also acts as a strange surrogate guardian who tries to show him the world beyond war, from amusement parks to the concept of a global peace plan. His relationship with Koko’s brother, Kasper Hekmatyar, is much more fraught. Kasper was responsible for selling the weapons that killed Jonah’s family, and he initially imprisoned and beat the boy. Yet, by Perfect Order, their interactions move toward a tense, businesslike respect. Jonah acknowledges that Kasper kept his promise to care for the orphans, leading Jonah to state that he might “start trusting” him, a significant move from his previous "hot-headed" hatred.

Jonah undergoes notable development. He matures from a reckless child with a death wish into a more calculated and stable operative. While he remains emotionally reserved, he gains a clearer sense of his own identity. This growth culminates in his reaction to Koko’s master plan. Upon learning of Jormungand, Jonah makes the difficult choice to leave her team, a decision driven by his independent principles. However, after a two-year time skip in which the world descends further into chaos, he ultimately rejoins Koko. This return suggests that despite his hatred for her methods, he has come to accept her worldview as the only possible path forward, demonstrating a complex and grim evolution from a passive child soldier to an active agent in a revolutionary scheme.

As a soldier, Jonah possesses notable abilities that far exceed his age. He is an expert marksman, typically wielding firearms such as a Magpul Masada rifle and a Sig Sauer handgun with lethal precision. His physical capabilities are peak human for his age, but his reaction time is superhuman, enabling him to dodge gunfire and track multiple targets in chaotic firefights. Beyond simple gunplay, he is highly proficient in guerrilla tactics, specializing in camouflage, stealth, and setting elaborate traps. He has demonstrated resourcefulness that borders on the extraordinary, such as deflecting an anti-tank missile with a well-thrown grenade. Furthermore, he possesses high physical stamina and an unusual resistance to sedatives, having awakened from a dose intended to keep him unconscious for hours in a matter of minutes. These skills, combined with his mentally hardened yet emotionally conflicted drive, make him one of the most formidable operatives in the series despite his youth.