Kenpachi has a wild and aggressive appearance, fitting with his personality. He wears his captain's jacket without sleeves, and with a more ragged look to it. He acquired his jacket from the previous 11th Division captain, whom he defeated and killed in a duel. He styles his hair into spikes with bells at the tips, which Tite Kubo has remarked makes his hair one of the most difficult to draw in the series. He also wears a special eye patch on his right eye created by the 12th Division to absorb the bulk of his power. Both of these are meant to give enemies an advantage, similar to his habit of fighting one-handed, as in an unhandicapped state he would defeat them so quickly that he would be unable to enjoy himself sufficiently to delve into a state of bloodlust, that being what he treasures most. He has a huge scar on the left side of his face, apparently gained well before his time in Soul Society (and even before finding Yachiru).

Despite his initial introduction as a lethal foe, Kenpachi later begins to play the role of the comical anti-hero in Bleach: though still self-centered and violent, his actions tend to be for the best and his relationship with his division and others is always portrayed comically. This comical shift is primarily centered around his appearances in the Bleach anime and omake stories, with the exception of the occasional diatribe between himself and Yachiru. He is depicted as having a very poor sense of direction, and is often depicted in omake stories asking his lieutenant Yachiru for directions to a particular place (who then randomly points in a direction).

Kenpachi lives for battle (evidenced by his method of attaining his rank) and enjoys a good fight more than anything. He even weakens himself in an effort to make any fight last longer. He also claims that injury and death are nothing but the price one pays for a good fight. Despite his group being the most bloodthirsty of the Gotei 13, they have their own code of ethics, different from the set rules of Soul Society, fitting with Kenpachi's portrayal as a free spirit. On various occasions, he is seen putting fun before work. Though he is portrayed as being bloodthirsty he will usually give up on a fight if his opponent can't fight back claiming that the fight is no longer fun, however he will kill without hesitation if his opponent insists on continuing.

Prior to entering Soul Society, Zaraki resided in District 80, the most lawless district surrounding Soul Society. He became very proficient with swordsmanship while he was there, and eventually adopting the district's name, "Zaraki", as his surname. After leaving the district he found a small girl who, despite her young age, did not fear his sword. Since she had no name, he named her Yachiru (やちる) in remembrance of the only person he ever admired. At the same time he also took on a name for himself: Kenpachi, the title bestowed upon the strongest swordsman, the one who has killed the most, and a tradition amongst captains of the 11th Division. Yachiru became inseparable from Zaraki from that point further, following him wherever he went, usually clinging to his back.

After some time had passed, Zaraki found his way into Soul Society and killed the previous captain of the 11th Division, thus gaining his seat in the Gotei 13. As a new captain, Zaraki was begrudgingly forced to learn kendo, though he made it a point to avoid using it in battle in order to prolong the experience of fighting as long as possible.

In an interview, Tite Kubo noted that he would like to go more into depth about Zaraki.

After Ichigo Kurosaki and his friends arrive in Soul Society, Kenpachi begins to hunt the strongest fighter in their group, and eventually battles Ichigo. During their fight, Ichigo becomes enough of a challenge that Kenpachi removes his eye patch, thus releasing the extra power it has been devouring. The battle ends in a draw, with Ichigo falling first and Kenpachi shortly after, both admitting defeat. Much later on, while searching for Ichigo with his friends in tow, they are headed off by 7th and 9th Division members. Kenpachi battles their captains Sajin Komamura and Kaname Tōsen respectively, defeating Tōsen and fighting off Komamura before Komamura runs away. He doesn't see Ichigo and his friends off when they leave the Soul Society. He tells Yachiru that he and Ichigo will certainly meet again because they are the only ones who are what they seem to be. Kenpachi also helps fight off the Bount invasion, and successfully defeats Maki Ichinose.

During the Arrancar arc, Zaraki appears to Ichigo as his instinct and desire to win, explaining to him that they were both the type of people who lived to fight battle after battle. After Orihime is taken to Hueco Mundo, Kenpachi arrives with Byakuya Kuchiki to retrieve Tōshirō Hitsugaya's group and bring them back to Soul Society. Later, in Hueco Mundo, Kenpachi comes to Ichigo's aid during his battle with the arrancar Tesla, dealing the arrancar a mortal blow with a single strike and then engaging Nnoitra Jiruga in battle. After sustaining several injuries, Kenpachi emerges victorious by using kendo, landing a massive blow to Nnoitra. Kenpachi then stands over Nnoitra's corpse and thanks him for a good fight.

Abilities

Kenpachi is the only captain of the Gotei 13 who doesn't know the name of his sword, nor can he use his bankai as a result. In addition, he never uses kidō and rarely uses flash steps, the only exception being in Bleach: Memories of Nobody as he is seen to appear behind one of the Blank officers during the battle, with him stating 'I dislike chasing people, but I'm not too bad at it'; the Bleach Official Bootleg databook ranks his talent in the former as zero. However, he more than makes up for his faults in sheer power. His spiritual pressure is such that, even when wearing the energy-sealing eyepatch, Kenpachi can fight on-par with other captain-level opponents, even when they release their zanpakutō in either shikai or bankai form. Its concentration is so great that it acts like armor against weaker opponents. During their first duel, he allowed Ichigo one free attack before the duel began. That attack failed to pierce his body, and actually cut Ichigo's hand.

Despite his seeming disregard for any strategy in his fights and his self-admitted aversion to thinking during battle, Kenpachi is adept at finding and exploiting weaknesses in his opponents' techniques. While he claims to have no sanity or common sense, Kenpachi is actually very perceptive and notices traits in people that others wouldn't notice. For example, he correctly singles out Kaname Tōsen and Gin Ichimaru as the only captains who are afraid to die. During his battles with both Kaname Tōsen and Nnoitra Jiruga, he formulates strategies to work around his disadvantages, such as losing all his senses or fighting an opponent with six arms.

Kenpachi has tremendous quantities of physical strength, most clearly evidenced by kicking Tōsen through a building in their battle, and grabbing Ichigo's giant sword barehanded and reeling both him and it in for an attack. His physical strength is matched by his endurance; Kenpachi has been shown to easily ignore most of the injuries he's sustained in battle, not suffering any debilitation despite having multiple slash wounds in his body. He even allowed himself to be stabbed just to grab Tōsen's blade and break his bankai's effect. The majority of his fight with Nnoitra was a one-sided brawl in Nnoitra's favor, with Kenpachi only taking things seriously when he finds himself in actual danger of dying from the sheer number of lacerations he had received. Kenpachi does not know the name of his zanpakutō, and is the only captain in the history of the Gotei 13 who cannot perform bankai. Despite not knowing its name, his zanpakutō is constantly released due to his immense spiritual pressure in the same manner as Ichigo's Zangetsu. The sword's appearance is a reflection of Kenpachi's own practice of weakening himself to fight: it is a seemingly worn-down and dull blade with a guard that extends inward from its center. The blade is much longer than that of a standard zanpakutō. Despite its appearance, it is easily capable of cutting through most objects. This is demonstrated when he stabs straight through Ichigo's zanpakutō and later slices a building in half with careless effort after releasing the full force of his spiritual power.

It appears that after his fight with Ichigo, Kenpachi wishes to learn more about his zanpakutō because he wants to become stronger and can identify with the pain of not having a name. However, he is not yet capable of communicating with his zanpakutō, and it is implied that he continually tries to learn from his zanpakutō so that he can achieve a new tier of power. Zangetsu

notes that Kenpachi's disharmony with his zanpakutō causes the two to diminish each other's power.