Sergeant Walker, an American military instructor, trains cadets at Watcher's Nest—including Misaki Kureha, Luxandra Frail, Suzanna Bluestein, and Kiri Marialate—under Lieutenant Commander Lyar von Ertiana's supervision. He oversees combat readiness and operational drills, extending his instruction beyond basic training to their ongoing development at the facility. Walker enforces a strict yet fair regimen, prioritizing discipline and resilience by pushing cadets past their perceived limits to prepare them for future challenges. He notably halts training for a demotivated Misaki until she independently regains her drive. Walker also appears in the sequel series "Misaki Chronicles."