Jean Kirstein hails from Trost District within Wall Rose. He initially enlisted in the military aspiring to join the Military Police Brigade for a secure life inside the inner walls, driven by pragmatic self-preservation. This outlook frequently clashed with Eren Yeager's fervent dedication to the Survey Corps during their cadet training in the 104th Training Corps, where Jean ranked sixth. His early demeanor was blunt, hot-headed, and cynical about defeating the Titans, marked by openly vocalizing frustrations even when provoking conflict. A pivotal shift occurred during the Battle of Trost District. Facing imminent Titan threats with depleted gear and no commanders, Jean first succumbed to despair. Witnessing Marco Bott's death profoundly altered him, catalyzing a sense of responsibility. He demonstrated emerging leadership by making the grim decision to capitalize on fallen comrades' sacrifices to guide surviving cadets to safety and resupply—an act that haunted him but underscored his capacity to prioritize group survival under extreme duress. This event solidified his choice to forgo the Military Police and join the Survey Corps. Throughout his Survey Corps service, Jean evolved into a dependable strategic leader, often assuming command in chaos. He rallied soldiers during Titan attacks in Trost, coordinated assaults against the Female Titan, and led squads during critical operations like the Raid on Liberio and the Battle of Shiganshina. His leadership emphasized pragmatism, risk assessment, and collective survival, contrasting with more reckless methods. Marco Bodt had earlier noted Jean's innate leadership potential, stemming from flaws that fostered keen situational awareness and judgment. Jean consistently upheld a strong moral compass, valuing human life and expressing deep aversion to unnecessary casualties. He criticized Commander Erwin Smith for withholding intelligence that cost lives and condemned Floch Forster's willingness to cause civilian deaths. During the Marley conflict, he reluctantly engaged enemy soldiers to protect allies but refused to harm child combatants like Gabi Braun and Falco Grice, explicitly rejecting execution suggestions. This conviction drove his vehement opposition to the Rumbling. While understanding the Yeagerists' motives to secure Paradis Island's future, Jean could not condone Eren Yeager's global genocide. He joined the alliance to stop the Rumbling, expressing profound distress over the mass slaughter of innocents, including refugees he had encountered. His decision stemmed from a resolve that avoiding complicity in atrocity outweighed personal safety or nationalistic interests. Physically, Jean matured significantly, growing to 190 centimeters with a more rugged appearance featuring longer hair and a goatee. He wore the standard Survey Corps uniform, later utilizing anti-personnel vertical maneuvering equipment and concealing his identity under a cloak and fedora during covert Marley operations. After the war, he remained with the Survey Corps, aiding its rebuilding efforts.