Haruaki Azuma is a B-rank Border agent and captain of Azuma Unit, having previously held A-rank status. He enlisted with Border shortly after the organization went public, roughly four years before Chika Amatori and Yūma Kuga, becoming Border's first Sniper. His initial unit soared to the No. 1 position within A-rank before its original members departed under unknown circumstances. Later generations of Azuma Unit included agents like Yukimaru Ichijō, Takaaki Katagiri, and Karin Yuitsuka, eventually solidifying with current members Tsuneyuki Okudera and Noboru Koarai, the latter having persistently sought Azuma's mentorship. Beyond his unit, Azuma trained numerous agents in sniping and strategy, including Mirai Hatohara, Reiji Kizaki, Tōru Narasaka, Isami Tōma, and Ren Tsukimi. He participated in an away mission to the Neighborhood and possessed knowledge of Cronin's true identity as a Neighbor, as well as Mirai Hatohara's defection.

Azuma possesses a tall frame with an average build, light skin, neck-length black hair, black eyes, pronounced tear-troughs, and a prominent nose. His trion body features a navy blue jacket with black accents, Border's logo on the sleeves, a light-colored shirt, black pants, and dark gray boots. He occasionally modifies his triggers for camouflage, such as changing Ibis to white in snowy conditions.

He exhibits a consistently calm and analytical demeanor, maintaining composure even in combat. Strategy and mentorship are his priorities, often guiding students through probing questions rather than direct instruction. This leadership style fosters deep loyalty, with agents across Border frequently seeking his directives. Azuma is genial and approachable, known for treating colleagues to meals and offering reassurance, such as calming Chika Amatori after an accidental training incident involving Ibis.

As a combatant, Azuma excels in sniping and tactical analysis. His proficiency includes predicting enemy movements, sniping through multiple walls using observational and topographical data, and rapidly switching targets. He primarily utilizes the powerful Ibis despite its low bullet speed, compensating with precision, and Lightning for its high fire rate. His trigger set also includes Dummy Beacon for radar deception, Bagworm for stealth, and Shield for defense. He is notoriously elusive, avoiding detection by top agents like Masataka Ninomiya and Masato Kageura due to his ability to suppress emotional cues. His strategic acumen was instrumental in defeating the powerful Neighbor Lamvanein during the Large-Scale Invasion, earning him individual and unit Distinguished Service awards.

Key operational involvements include the Border Enlistment Arc, where he instructed new recruits, reassured Chika after her trion test incident, and deduced Tamakoma Branch's tactical concealment of her abilities. During the Large-Scale Invasion Arc, he led his unit against Aftokrator's forces, analyzed Rabbit trion soldiers, and devised the strategy that defeated Lamvanein through coordinated attacks. In the B-Rank Wars, he participated in multiple rounds, bailing out early in Round Two due to focused enemy fire. In Round Four, he employed environmental tactics like snow camouflage, sniped Osamu Mikumo through walls, and survived until the match end. He later strategized against Tamakoma Second and others in Round Seven. He also attended the emergency meeting during Galopoula's Blitz, suggesting leveraging Tsukihiko Amō's Side Effect for intelligence gathering rather than combat.

Outside Border, Azuma is a postgraduate engineering student researching trion composition and military history. His hobbies include fishing, camping, sashimi, tempura, and mahjong. He holds a driver's license and is officially profiled as "low-tension, long-range, long-hair".