Borsalino, widely recognized by his alias Kizaru, holds the rank of Admiral in the Marines. He remains one following the timeskip, becoming the last serving Admiral from the original trio after Kuzan resigned and Sakazuki ascended to Fleet Admiral. His Marine career began at age 26 alongside Sakazuki, both trained by Zephyr. During this early period, he consumed the Pika Pika no Mi (Glint-Glint Fruit), a Logia-type Devil Fruit. This grants him the power to generate, manipulate, and transform his body into light, enabling movement and attacks at light speed, intangibility, and techniques like energy blasts, light-speed kicks, and forming a durable light sword. Dr. Vegapunk studied these abilities, replicating them for Pacifista units and Seraphim technology.

Kizaru consistently exhibits a relaxed, calm, and seemingly absentminded personality, maintaining an easygoing demeanor even in intense conflicts. His speech is characteristically slow, often drawing out syllables, beginning sentences with elongated expressions like "ooh," and ending them with rhetorical particles such as "ne." He adheres to a principle called "Unclear Justice," representing a neutral stance between his fellow Admirals' extremes. This philosophy positions him as a cog within the Marine structure, executing orders without deep personal investment in their moral implications. Despite this apparent apathy, he demonstrates loyalty to the World Government, fulfilling duties like responding to threats against Celestial Dragons.

His significant military engagements include acting as a secondary antagonist during the Sabaody Archipelago Arc, where he overwhelmed multiple members of the Worst Generation and the Straw Hat Pirates, capturing 500 pirates afterward. He participated as a major combatant against Whitebeard's forces at the Marineford War. Later, during the Egghead Arc, he led the Marine assault on Egghead Island under orders to eliminate Dr. Vegapunk. This mission forced confrontations with Sentomaru—whom he trained and considers family—and Vegapunk, a long-time friend. These clashes caused visible emotional strain, culminating in an uncharacteristic outburst against Fleet Admiral Sakazuki after Vegapunk's death and covert assistance to an exhausted Monkey D. Luffy by providing food using his light-speed capabilities.

Kizaru shares key relationships: he mentored Sentomaru from childhood after encountering him during a mission with Vegapunk, training him extensively in combat and fostering a familial bond where Sentomaru refers to him as "uncle." His decades-long association with Dr. Vegapunk involved collaborative research on his Devil Fruit powers, making his role in Vegapunk's assassination profoundly conflicting; Kizaru expressed overt regret and sorrow during the event. His dynamic with Sakazuki grew tense following the Egghead mission, marked by resentment over the emotional toll of his orders.

Physically, Kizaru is exceptionally tall with a slim build, short curly black hair, a thin beard, and distinctive slanted eyes often concealed behind amber-tinted sunglasses. He typically wears a yellow pinstriped suit with the Marine coat draped cape-style, later adopting a black-and-yellow striped suit during the Egghead Arc.

His combat style heavily utilizes his light-based powers. Key techniques are "Yata no Kagami" for light-path transportation, "Ama no Murakumo" for generating a light sword, and "Yasakani no Magatama" for firing volleys of destructive light orbs. These abilities require brief momentum buildup for light-speed movement, creating exploitable openings, and his light beams travel strictly linearly. Like all Devil Fruit users, he remains vulnerable to seawater and sea prism stone.