Admiral Kizaru, whose real name is Borsalino, is a towering and imposing figure within the Marines, holding one of the three highest-ranking Admiral positions. He is a middle-aged man with a lined face and a thin beard, typically dressed in a sharp yellow-striped suit. He wears a white Marine coat draped over his shoulders like a cape, leaving his arms free, and complements his outfit with pure white shoes and gold-amber tinted sunglasses. A small black Den Den Mushi, used for wiretapping, is often seen on his left wrist like a watch. He is almost always seen with a relaxed, shrewd smile on his face.

Kizaru's personality is defined by a profound and almost unnerving sense of calm. He speaks very slowly, often drawing out the last word of his sentences, and rarely, if ever, appears shocked or excited, even in the most chaotic or surprising situations. This laid-back demeanor often borders on absentmindedness, as he has been known to make careless errors, such as using excessive force by accident or trying to make a phone call with a device meant only for eavesdropping. Despite his casual and sometimes detached attitude, he possesses a ruthless and merciless side when dealing with pirates. He shows little hesitation in using deadly force, as seen when he casually suggested shooting the giant warrior Oars Jr. through the head or when he decided to capture the retired Silvers Rayleigh, arguing that his past crimes as a member of the Roger Pirates could never be forgiven. He often remarks that the abilities of his opponents are "frightening" or "scary," but his deadpan expression and slow tone make it unclear whether he is genuinely intimidated or simply mocking them.

Kizaru adheres to a personal philosophy known as "Unclear Justice." Unlike his fellow admirals who follow more defined moral codes like Absolute Justice or Lazy Justice, Kizaru's approach is ambiguous and pragmatic. He views himself as a cog in a machine, preferring to follow orders rather than issue them, which allows him to avoid personal moral responsibility for his often harsh actions. This makes him a particularly dangerous and unpredictable force, as he can shift from being casually indifferent to lethally efficient without any change in his demeanor. He is not driven by a passionate ideology but by duty, and he will carry out his missions, even against former friends, with a detached sense of obligation.

In the story, Kizaru serves as one of the Marines' ultimate weapons, a nearly unstoppable force sent to deal with existential threats to the World Government. He was first deployed to the Sabaody Archipelago after the Celestial Dragon Charloss was assaulted by Monkey D. Luffy. There, he effortlessly defeated several of the eleven Supernovas, demonstrating a terrifying gap in power. He played a major role in the Paramount War at Marineford, where he clashed with Whitebeard and his commanders, using his abilities to obstruct Luffy's attempts to rescue his brother Ace. Years later, he is dispatched to Egghead Island with the mission to assassinate his old friend, the brilliant scientist Dr. Vegapunk, leading to a direct confrontation with the now-Emperor Luffy and the Straw Hat Pirates.

Kizaru has several key relationships that define his role. He holds a casual and respectful relationship with his fellow admirals, particularly Akainu, who became Fleet Admiral. He is a confidant to Akainu, offering counsel, and is one of the few people who can speak to him informally. His most significant relationship is with Vegapunk and the Vegapunk's bodyguard, Sentomaru. Kizaru has known them for many years and personally trained Sentomaru, who affectionately calls him "Uncle." This history makes his mission to Egghead a deeply conflicted one, as he is forced to carry out orders that require him to harm people he once considered close friends. He also has a notable past with Bartholomew Kuma and Jewelry Bonney, having spent a year on Egghead overseeing Kuma's transformation into a cyborg and forming a temporary, almost friendly bond with them.

While Kizaru does not undergo a dramatic personality shift, the Egghead Arc provides significant development by placing his "Unclear Justice" under immense strain. For the first time, his detached, duty-bound persona cracks as he expresses visible regret and reluctance about having to kill Vegapunk, a personal friend. He admits he does not wish to carry out the mission but feels he has no choice as a cog in the machine. This internal conflict adds a layer of tragedy to his character, showing that even a seemingly unflappable force of nature is not immune to the emotional toll of his duties.

Kizaru's notable abilities are among the most powerful in the world. He is a user of Busoshoku Haki, which allows him to strike the true bodies of Logia users, and Kenbunshoku Haki, which grants him heightened awareness. However, his primary power comes from the Pika Pika no Mi, a Logia-class Devil Fruit that allows him to create, control, and transform into light. This grants him near-intangibility, as physical attacks pass through his light form, and allows him to move and attack at light speed, making him one of the fastest characters in the series. He can fire powerful, destructive lasers from his hands and feet, create a sword of pure light to duel skilled swordsmen, and perform devastating area-of-effect attacks like Yasakani no Magatama, where he unleashes a torrent of light particles. His signature movement technique, Yata no Kagami, involves him reflecting himself between surfaces as a beam of light. His combination of overwhelming speed, destructive power, and a cold, unshakeable resolve makes him one of the most formidable antagonists in One Piece.