Haruaki Azuma is the captain of Azuma Unit, a B-Rank squad within the Border organization, where he operates as a Sniper. He is a tall young man of average build with pale skin, neck-length black hair, and black eyes, the most distinctive features of his face being pronounced tear troughs and a large, straight nose. When in his Trion body, he wears a navy blue long-sleeved jacket with black stripes, which is left open over a light-colored shirt with a slit collar and a lace tied in a bow. His uniform is completed with black pants and dark gray boots, though he is known to modify the color of his gear for camouflage, such as changing his Ibis rifle to white to blend in with snowy terrain.

Azuma is a very self-possessed and analytical individual, able to retain complete lucidity even in dire combat situations. This calm demeanor and sharp mind have earned him the trust and respect of numerous agents throughout Border. He is known to be a genial person who often wears a faint smile, and he is quite popular, occasionally treating colleagues and students to meals. Although he appears serious, he can be reassuring and even display a subtle sense of humor, as seen when he calmly told a worried Chika Amatori that it was alright to shoot through a wall during a training accident because it would simply be considered an accident. His mentees know him to be slier and more capable of underhanded tricks than his widespread image might suggest. As a teacher, his style is to impart his core teachings and then let his students find their own answers, limiting himself to asking guiding questions and stepping in only rarely to state a preference.

Azuma joined Border soon after the organization went public, roughly four years before the main story begins, and holds the distinction of being Border's first Sniper. His original unit rose to become the number one A-Rank squad. Over time, many of its members left to form their own teams, and Azuma eventually reformed the unit with his two current teammates, the Attackers Noboru Koarai and Tsuneyuki Okudera, with the explicit goal of fostering their growth. Beyond his own squad, he has mentored a great number of agents, including prominent figures such as Reiji Kizaki, Toru Narasaka, and Masataka Ninomiya, making him one of the most influential teachers in the organization. He was selected for an away mission to the Neighborhood and is one of the few agents aware that Mirai Hatohara, a former student, defected to the other world.

During the Large-Scale Invasion arc, Azuma demonstrated his value as a field commander. After his teammates were captured or forced to bail out by a new type of Trion soldier called a Rabbit, he assumed control over the nearby B-Rank teams. When the powerful Neighbor Lamvanein appeared, Azuma quickly analyzed his trigger and devised a strategy. He coordinated the B-Rank agents on the ground with arriving A-Rank units to capitalize on their numerical advantage and diffuse the enemy's attention, successfully drawing Lamvanein into a trap that led to his defeat. For his actions, he received an Outstanding Distinguished Service award.

In the B-Rank Rank Wars, Azuma serves both as a competitor and as a popular commentator whose precise and insightful analysis draws in even top A-Rank agents to watch. As a fighter, his role as captain often takes a backseat to his primary goal of training Koarai and Okudera. He allows them to formulate the basic strategy, referring to himself as a pawn and only offering his opinion when asked, though his actions in battle speak to his ace-level abilities. He is notoriously elusive, to the point where top fighters like Masataka Ninomiya and Masato Kageura prefer to hide rather than risk being picked off by him. His ability to fight without detectable emotion makes him one of the only two people in Border who do not trigger Kageura's Side Effect, which senses bloodlust.

Azuma's abilities as a Sniper are legendary. He is a master of stealth and can hit moving targets from great distances, switch targets at incredible speed, and even snipe through multiple walls by combining observational data with detailed topographical information. He is proficient with all three main Sniper triggers. He primarily uses the high-power Ibis, compensating for its low bullet speed by accurately predicting his target's movements. He also makes devastating use of Lightning, employing its high rate of fire to shoot down incoming Meteor bullets mid-air or strike the same opponent repeatedly in different spots. To enhance his tactical game, he uses Dummy Beacon to clutter enemy radar with decoy signatures and Bagworm to conceal his own position. Outside of combat, Azuma is a postgraduate engineering student conducting experiments on trion composition, and he has also researched military history and tactics. His personal interests include fishing, camping, sashimi, tempura, and mahjong.