Miles Mayer is a longtime member of the Monroe Family and serves as Daniel Monroe’s right-hand man. He is a hefty man, standing 1.91 meters tall, with light blonde hair, a thin light-colored mustache, and brown eyes. His calm and steady temper contrasts with the violent world of Ergastulum; he is known to enjoy teasing younger members of the family, indicating a dry, occasionally playful demeanor.

Miles’s primary motivation is loyalty to Daniel Monroe and the Monroe Family. He consistently puts himself in harm’s way to protect Monroe and the family’s interests, once stating that he does not care if he dies as long as Monroe and another subordinate are safe. He was one of only two people present during a C/3 Twilight attack years earlier who escaped relatively unharmed, demonstrating his resilience and experience in dangerous situations.

In the story, Miles operates as a senior enforcer and advisor within the Monroe household. He is a supporting character who often handles security and crisis management. When the Striker—a member of the Third Destroyers—attacks the Monroe estate, Miles attempts to buy time, showcasing his willingness to sacrifice himself. His relationship with Daniel Monroe is one of deep mutual trust and long-standing service. Additionally, he develops a paternal bond with Worick Arcangelo, acting as a father figure according to later manga developments, which adds a gentler dimension to his character.

Miles does not possess superhuman abilities; he is a normal human in a world where “Twilights” (enhanced individuals) exist. His notable assets are his unwavering loyalty, his level-headedness under pressure, and his formidable physical presence. He remains a steady, reliable figure within the Monroe Family, though his character sees limited growth as he is primarily defined by his devotion to Monroe and his readiness to face lethal threats.