Keith Shadis served as the 12th Commander of the Scout Regiment, resigning after repeated failures and a crisis of confidence. Under his leadership, expeditions beyond the walls yielded minimal success, marked by high casualties and little progress. He dismissed innovative strategies from subordinates like Erwin Smith, confident in his own methods. Returning from a failed expedition in 845, a grieving mother confronted him, demanding justification for her son's death. Shadis broke down, confessed his inadequacy, and resigned immediately, recommending Erwin Smith as his successor while acknowledging he was not one of the "special people" capable of greatness. His worldview was deeply shaped by his relationship with Grisha Yeager. Discovering Grisha outside Wall Maria in 832, Shadis brought him to Shiganshina and explained life within the walls. Grisha's praise of Shadis's ideals fueled his arrogance and belief in his own uniqueness, particularly after Grisha stated only "special people" should join the Scouts. However, seeing Grisha prioritize family over the Scout Regiment, and later hearing Carla Yeager declare that one need not be "special" to matter ("He’s already great because he was born into this world"), planted seeds of doubt in Shadis about his own significance. After resigning, Shadis became head instructor of the 104th Cadet Corps, adopting a harsh and intimidating demeanor to break down trainees and build resilience. He deliberately frightened cadets during initiation, physically confronting some like Jean and Connie for perceived weaknesses. He recognized exceptional determination in cadets like Eren, Mikasa, Annie, Bertholdt, and Reiner, choosing not to intimidate them. Fearing Eren Yeager's self-destructive drive mirrored his own past failures, Shadis sabotaged Eren's ODM gear during training, hoping to force him out of the military. He abandoned this effort upon witnessing Eren's unwavering determination during a retest. During the Marleyan invasion of Paradis and the rise of the Yeagerists, Shadis was violently overthrown as instructor by his former cadets, who declared his methods obsolete. Cast aside, he observed events from the periphery, reinforcing his self-perception as a bystander. Witnessing his former trainees—including Armin, Mikasa, and Jean—unite with Marleyan warriors like Annie and Reiner to stop Eren's Rumbling reignited his sense of purpose. Inspired by their selfless mission, he intervened to aid their escape from Yeagerist forces. His final act involved collaborating with Theo Magath, a Marleyan military leader who mirrored Shadis's role as a mentor burdened by past failures. Recognizing their shared purpose in protecting their students, they infiltrated a Yeagerist-controlled port. To prevent the Yeagerists from using a ship to pursue the alliance, Shadis and Magath detonated explosives aboard the vessel, sacrificing themselves in the blast. Magath, acknowledging their parallel lives, asked Shadis's name moments before their deaths, granting him a final moment of recognition. This sacrifice successfully delayed the Yeagerist pursuit, crucially aiding the alliance's efforts, though his role remained largely unknown to those he saved.