Kazuma is a central supporting figure, known primarily as the oldest, most trusted, and most important Regalia of the war god Bishamonten. He holds the position of her exemplar, serving as her guide and the strategist who coordinates all of her other Regalia in battle. His physical appearance is that of a young man with short brown hair and dark green eyes, usually seen wearing a formal suit and a pair of thick-rimmed glasses. As a Regalia, when called by his master using his vessel name, Chouki, he transforms into a cherry blossom-shaped earring. Before becoming a blessed vessel, his form was that of a small thorn or nail. His own name, Kazuma, ends with the character for "hemp" (Ma), a permanent reminder of a tragic event in his past.

In terms of personality, Kazuma is consistently calm, serious, sensible, and deeply devoted to his master, whom he affectionately calls by the pet name Veena. He is extremely loyal, responsible, and trustworthy, carrying out his duties with a high degree of professionalism. Beyond his stern exterior, he is a kind individual and a good teacher, as demonstrated when he willingly takes Yukine under his wing to instruct him in the techniques of a blessed Regalia. His polite demeanor extends to everyone, even his master's enemies, and he holds himself to a strict moral code that places great importance on repaying debts, particularly the one he owes to the god Yato. Despite his serious nature, he possesses a comical side, often expressed through subtle teasing or revealed in embarrassing moments, such as when it is discovered his smartphone is full of candid photographs of Bishamonten. This collection implies romantic feelings for his master that he does not act upon, possibly due to the boundaries of their master-servant relationship or the prohibitions placed upon the Seven Gods of Fortune. He also demonstrates a colder, pragmatic side, believing that a Regalia must suppress feelings of guilt to avoid blighting their god, a philosophy he imparts to Yukine.

Kazuma's primary motivation is the protection and well-being of Bishamonten, a goal he pursues with absolute dedication, even if it requires morally questionable actions. His role in the story is multifaceted. He acts as the steadfast right hand to Bishamonten, attempting to manage her large and often unruly clan of Regalia. He also functions as a bridge between Bishamonten and Yato, secretly aiding his former enemy out of a sense of profound debt and loyalty. This stems from a key event in his past when he secretly begged Yato to slay Bishamonten's previous clan of Regalia, the Ma clan, which had become corrupted and was killing her from within. This act saved Bishamonten's life but made Yato her sworn enemy, a secret Kazuma carries for centuries. Later, he becomes a mentor to Yato's Regalia, Yukine, teaching him how to master his abilities as a blessed vessel.

His key relationships define his journey. His bond with Bishamonten is the most central, characterized by his unwavering loyalty, deep affection, and his willingness to confront or deceive her for her own good. He feels a significant debt to Yato, referring to him as a benefactor and helping him on multiple occasions, which later strains his relationship with his master. He develops a respectful teacher-student dynamic with Yukine, though this is tested when Kazuma uses a truth spell on him, leading Yukine to declare him an enemy. He also treats Hiyori Iki with trust and respect, recognizing her importance to Yato. Throughout the story, Kazuma undergoes significant development. Initially defined by his guilt over the destruction of the Ma clan and his desire to atone, he eventually becomes a more proactive agent. In a dramatic turn, he chooses to leave Bishamonten's service and become a stray Regalia, or Nora, for Yato under the name Kazune (vessel name Rekki) to gain the power and freedom necessary to help defeat a powerful sorcerer who threatens both his master and Yato.

As a Regalia, Kazuma possesses numerous notable abilities. His primary power in his earring form is exceptional tracking and navigation, allowing him to precisely coordinate the attacks of all of Bishamonten's other Regalia. As a blessed vessel, he holds considerable power and can use a variety of spells. These include Umbra, which allows him to manipulate his surroundings; Restraint, which binds a target in invisible chains; and Resound, which compels a target to speak the truth. He is also highly skilled in creating a Borderline, a barrier that separates the near shore from the far shore. As Yato's Regalia, he takes the form of a tracksuit-like divine garment and a versatile weapon that can shift between a katana and a bow, demonstrating his adaptability and high level of skill in combat.