Armin Arlert hails from the Shiganshina District within Wall Maria. His grandfather's forbidden book about the outside world ignited his lifelong fascination with exploring beyond the walls, yearning to see oceans and volcanic landscapes. This curiosity led to childhood bullying, as other children branded him a heretic. Physically frail and timid, he relied on friends Eren Yeager and Mikasa Ackerman for protection, fostering deep bonds but also enduring shame and low self-esteem over his perceived burden on others. Following the fall of Wall Maria and his grandfather's death during the mission to retake it, he enlisted in the 104th Training Corps alongside Eren and Mikasa. Despite ranking near the bottom in combat skills, his exceptional intellect and strategic aptitude earned him recognition. His tactical contributions proved pivotal in critical operations: devising the plan to seal Trost District's breached gate using Eren's Titan strength, identifying Annie Leonhart as the Female Titan through careful observation of her gear, and formulating the strategy to capture her. During the battle to reclaim Shiganshina District, Armin executed a self-sacrificial plan to defeat Bertholdt Hoover's Colossal Titan, resulting in near-fatal burns. Captain Levi's controversial decision to inject him with Titan serum saved his life but transferred the Colossal Titan's power to him. This triggered profound psychological turmoil, mixing gratitude for survival with intense guilt over Commander Erwin Smith's death, anger towards Levi's choice, and horror at consuming Bertholdt alive to inherit the power. After inheriting the Colossal Titan, Armin's physical appearance matured, and he gradually developed confidence in his leadership capabilities. He was appointed the 15th commander of the Survey Corps by Hange Zoë. During the raid on Liberio in Marley, he utilized his Titan form to destroy the Marleyan fleet and harbor, emerging visibly distressed and tearful over the civilian casualties inflicted. His relationship with Eren fractured as Eren pursued the Rumbling independently. Armin initially hesitated to confront Eren, rationalizing his inaction through a lingering victim mentality stemming from the serumbowl incident and feeling powerless over his transformation. As Eren activated the Rumbling, Armin shifted towards proactive leadership. He collaborated with former enemies, including Annie Leonhart and Reiner Braun, to form an alliance against Eren. Within the Paths dimension, he engaged in a final conversation with Eren using the Founding Titan's power, revisiting landscapes from Armin's book symbolizing their lost dreams, culminating in a shoreline transformed into blood. Armin expressed outrage at Eren's genocide but ultimately accepted shared responsibility for the path leading to it, acknowledging his role in shaping Eren's destructive worldview through their shared dream of freedom. He thanked Eren while condemning his actions, pledging to bear the burden of their collective sins. Armin possesses a complex personality marked by analytical brilliance, deep loyalty, and moral conflict. He demonstrates exceptional skill in formulating unconventional strategies, often relying on psychological manipulation and calculated risks based on intuitive hunches. He strongly believes overcoming monstrous adversaries requires sacrificing one's humanity, admiring figures like Erwin Smith for their willingness to make ruthless choices. Consequently, he crafts morally ambiguous plans that surprise comrades. Despite this pragmatic approach, he retains a core of empathy and kindness. Killing causes him significant distress, manifesting in physical reactions like vomiting, and he rejects absolute labels of "good" or "evil," viewing morality as subjective. He values human connection, maintaining visits to Annie during her crystallization and later forging a romantic bond with her as they worked towards peace. His leadership style evolved from anxiety and self-doubt into a more resolute, albeit burdened, commitment to creating a better future. Following Eren's death, Armin claimed credit for killing him to protect Mikasa and facilitate post-conflict negotiations. He assumed the role of peace envoy, advocating for reconciliation between Eldia and the surviving outside world.