John S, whose full name is John Steinbeck, is a character introduced in the second season of the series as a member of the North American organization known as the Guild. He is a young man of twenty-one years with a lean build, standing at 175 centimeters tall. His appearance is distinctive and rustic, marked by short blonde hair, blue eyes, and a flat cap he wears atop his head. His attire typically consists of a white shirt with rolled-up sleeves, blue overalls secured with a black belt, and dark boots. He is often seen carrying a raw potato and a navaja, a folding knife he uses as a tool to activate his special ability.

John Steinbeck's personality is a blend of easygoing charm and ruthless pragmatism. He generally presents himself as a relaxed and casual individual, often making light conversation with his partner, Lovecraft, without worrying if enemies are listening. This relaxed demeanor, however, can lead to overconfidence, as he has been known to divulge details about his abilities to opponents, which can prove to be a tactical error. Despite a tendency to complain about chores and try to avoid extra work, he is far from lazy and is fully capable of carrying out the dangerous missions assigned to him. While he can be polite and almost kind in his interactions, he harbors no qualms about using brutal force against his enemies, showing a complete lack of regard for their well-being. The core of his morality and his primary driving force is not a sense of justice or ambition, but a deep and abiding devotion to his large, impoverished family back home.

Steinbecks motivations are rooted in poverty and familial duty. Prior to joining the Guild, he worked as a poor farmer in North America. He enlisted with the Guild solely for the substantial financial compensation it provided, which he used to support his family. This singular goal defines his actions; he is willing to perform any dirty or dangerous task necessary to ensure his family is provided for, with a particular soft spot for his younger sister, whom he spoils constantly. Consequently, he holds a deep-seated hatred for the Guilds leader, Francis Scott Key Fitzgerald, not necessarily as a person, but for his endless ambition, arrogance, and belief that money can solve everything. He views Fitzgerald as a capitalist who does not understand the true value of family or the struggle against poverty.

In the story, John S plays the role of a supporting antagonist and a key operative for the Guild during their conflict with the Armed Detective Agency and the Port Mafia. He frequently works in tandem with his partner, H.P. Lovecraft, acting as the more chatty and strategic half of the duo tasked with capturing enemy combatants. Early in the arc, he and Lovecraft ambush members of the Agency, where he showcases his ability and nearly succeeds in capturing them before being outsmarted and ultimately arrested after a truck crashes into them. His role becomes significantly more crucial during the Guild's emergency plan to terrorize Yokohama. In this plot, he uses his ability to connect the plants across the entire city to the captive ability user Q. This connection allows any harm done to the city's flora to be transferred to Q, activating Qs curse on the perpetrator and causing widespread chaos.

His key relationships are defined by practicality and deep-seated resentment. His partnership with Lovecraft is his most prominent alliance; he considers the eldritch being one of his few friends, trusting him as a teammate despite his bizarre nature. The most complex relationship is with his boss, Fitzgerald. While he obeys orders to achieve his goal of supporting his family, he despises Fitzgerald personally. After the Guild is defeated and Fitzgerald goes missing, John temporarily stays behind to lead the remnants of the organization, not out of loyalty, but to pacify the internal rebellion and protect his source of income. When Fitzgerald later resurfaces to rebuild the Guild, John observes from the shadows with a fierce expression, vowing to crush Fitzgeralds ambitions so that they can become equals, or perhaps so Fitzgerald can finally understand what it means to lose everything.

John S develops from a seemingly simple hired gun into a more complex figure of resilience and quiet defiance. While he begins as a confident agent of the Guild, his defeats and the eventual collapse of the organization force him to show a more cunning and independent side. Rather than abandoning the fallen group, he chooses to stay, demonstrating a sense of responsibility for those who remain. His hatred for Fitzgerald, initially a background annoyance, becomes a defining motivation for his future actions, transforming him from a subordinate into a potential rival who is willing to lead a faction specifically to oppose the man he hates, all for the sake of his family.

John S possesses the ability named The Grapes of Wrath. This power allows him to grow razor-sharp grapevines from his own body, typically by planting a seed into his bloodstream. By grafting these vines onto other plants, he can extend his control to all flora in the surrounding area, turning the entire vicinity into an extension of his own body. He can use these plants to capture and restrain enemies with tremendous strength, create shields to block attacks like speeding vehicles, and even sense vibrations in the ground to track movements. A more advanced and sinister application of his ability is sensory sharing; by connecting his vines to another persons body, he can transmit physical sensations, such as pain, between himself, the plants, and the target. This was the core mechanism of the Guilds plan to weaponize Qs curse across all of Yokohama.