Jean Kirstein hails from Trost District within Wall Rose. Driven by pragmatic self-preservation rather than idealism, he enlists in the 104th Training Corps aiming for the safety of the Military Police Brigade. He ranks 6th overall, demonstrating proficiency with vertical maneuvering equipment and tactical assessment. His early personality is blunt, hot-headed, and cynical regarding humanity's fight against Titans, leading to frequent clashes with idealistic peers like Eren Yeager. He also develops an attraction to Mikasa Ackerman, fueling his rivalry with Eren. A pivotal shift occurs during the Battle of Trost District. Faced with imminent Titan invasion and dwindling resources, Jean initially succumbs to despair before later assisting Mikasa in rallying leaderless cadets for a desperate charge toward headquarters. Forced to exploit comrades' deaths as a diversion for survival, the horror of this act showcases his emerging capacity for difficult leadership choices under extreme duress. The traumatic death of his close friend Marco Bott catalyzes his transformation, compelling him to honor Marco's belief in his leadership potential by abandoning his Military Police aspirations and joining the Survey Corps. Within the Survey Corps, Jean evolves into a strategic and level-headed commander. His inherent pragmatism and fear, once perceived as weaknesses, refine his ability to assess risks and prioritize group survival, evident during the 57th Expedition where he coordinates an attack on the Female Titan despite personal terror. His leadership qualities are formally recognized; he commands squads during critical operations like the Raid on Liberio and the Battle of Shiganshina. He increasingly relies on intellect over emotion, deferring to Armin Arlert's strategic mind during the Return to Shiganshina arc and motivating Eren to leverage the Attack Titan's power. Jean consistently grapples with the moral weight of violence. While reluctantly accepting killing enemy soldiers to protect allies, he staunchly refuses to harm civilians or child combatants, opposing Floch Forster's tactics in Liberio and rejecting executing Gabi Braun and Falco Grice. His aversion to human conflict intensifies during the Yeagerist uprising and the Rumbling. Though understanding the Yeagerists' motives to secure Paradis Island's future, he cannot condone global genocide or the killing of former comrades opposing it. He plays a decisive role in forming the Alliance to stop Eren Yeager, sacrificing his lifelong dream of peace and safety, culminating in his instrumental act of blowing the nape of the Founding Titan to halt the Rumbling. Four years after enlisting, Jean grows taller (190 cm), sports a goatee, and wears longer hair. During undercover operations in Marley, he utilizes anti-personnel vertical maneuvering equipment. His character arc concludes tragically yet resolutely when temporarily titanized during the Rumbling's final stages; he accepts his fate without regret, acknowledging his sacrifices prevented global annihilation. Connie Springer later credits Jean's initial decision to join the Survey Corps as the inspiration that gave him and Sasha Blouse the courage to follow, underscoring Jean's enduring legacy as an unsung but pivotal leader.