Prior to attaining his title as Kenpachi, Zaraki was a resident of the Rukon District, "Wandering Soul City". Zaraki's ambitions were warped in his youth in his attempts to defeat the first Kenpachi, Yachiru. Continued defeat by Yachiru Kenpachi left Zaraki craving the title and instilled a constant need for battle and a worthy opponent. As Yatchiru considered Zaraki to be one of the only spirits to ever offer her a challenge as worthy opponent, she retired her position shortly after a battle in which Zaraki actually managed to scar her. With no one left to fight Zaraki wandered the Rukon District shiftless, in his travels he encountered a small girl who seemed to not fear him and who was fascinated by blood shed, Zaraki took the girl on as an apprentice and named her "Yachiru", after his idol. Overtime Zaraki became a surrogate father figure and idol to Yachiru and a powerful spirit in her own right. The two wandered the Soul Society for years. Seeking worthy foes. In his attempts to find a worthy foe Zaraki met Ikkaku Madarame, a wandering spirit who like him lived to prove his worth against stronger foes. Ikkaku attempted to kill Zaraki but was completely over-powered with minimal effort on Zaraki's part. Zaraki saw some potential in Ikkakku and spared him in hopes he would get stronger and one day offer him a real challenge. Ikkaku became as obsessed with defeating Zaraki as Zaraki was with defeating Yachiru Kenpachi and vowed to one day find and defeat him.
Squad 11 One day in his travels Kenpachi learned of a Captain in the Gotie 13 called, Gosuke Kiganjo Kenpachi, who was the 10th titled "Kenpachi" to inherit the title after Yachiru Kenpachi's retirement. Though Zaraki had spent most of his life coming to terms with being denied a chance to fight Yachiru Kenpachi again the opportunity to defeat the current holder of her title was an opportunity he could not pass up and so after years of training challenged Gosuke Kiganjo Kenpachi to a fight to the death. Zaraki made good on his goals and slaughtered Gosuke Kiganjo inheriting the title of Kenpachi and even the position of Captain, for Gosuke Kiganjo had killed his superior officer in the 11th division of the 13 Gotie and had imposed a rule upon the squad allowing a captain to be replaced by anyone who beat him in formal combat. Upon defeating his foe and inheriting his title Zaraki had inadvertently taken on the title of Captain. When the Soul Society's council, Central 46, informed Zaraki he would be considered a captain from that point on if he was willing to take on the responsibility and be given control of the entire 11th division Zaraki accepted.
Kenpachi would eventually find out that the 13 Gotie's 11th division was founded by Yachiru Kenpachi and that while she had retired from it she was currently the head of the 4th division, working under her original name Retsu Unohana. The 11th division was always considered the 13 Gotie's most kill happy squad, however Kenpachi was less than impressed with his new troops, claiming a little girl like Yachiru could take them on with ease and vowed to whip the entire squad into shape, following up his boast by formally appointing Yachiru Kasajishi his Lieutenant. Eventually Ikkaku Madarame joined the 11th division along with his partner Yumichika Ayasegawa, Ikkaku Madarame had never given up on his goals of defeating Zaraki and Kenpachi accepted him knowing well the urge to defeat worthy opponents and keeping Ikkaku around to keep himself from getting weak. Though Ikkaku attempted to become Lieutenant, Kenpachi kept Yachiru as his Lieutenant, never backing down from his claim that she was stronger than all the 11th squad put together, a claim Yachiru was more than happy to prove over and over again to the squad. Even though Kenpachi considered Ikkaku less powerful than Yachiru he appointed him and Yumichika as his top men just below Yachiru.
Soul Society arc In Bleach's Soul Society arc, Soul Reaper Rukia Kuchiki had been sentenced to summery execution by Central 46 for less than specified reasons that made several Captains uneasy. Kenpachi concerned himself little with decisions of Central 46 unless they affected him specifically and so simply viewed the controversial judgment as meaningless politics, however he became greatly invested with events when Rukia's friends, Ichigo Kurosaki, Orihime Inoue, Yasutora "Chad" Sado and Uryū Ishida from the world of the living, broke into the Soul Society to rescue her. The intrusion was considered invasion by central 46 and Head Captain Yamamoto insisted that the threat was to be taken very seriously and the invaders were to be killed quickly. Kenpachi eagerly went to engage the invaders in hope they were strong enough to justify breaking into the Soul Society. Kenpachi would soon encounter Ichigo in an one on one duel. Though Ichigo had managed to defeat Iakkaku he had been warned about Captain Zaraki as the Soul Society's fiercest warrior. Unable to avoid the fight once Zarakai found him Ichigo engaged Kenpachi in combat in order to get passed him and save Rukia.
Though Ichigo showed minor promise, Zaraki considered him an extremely disappointing battle. The battle with Kenpachi Zaraki though was what would first prompted Ichigo to dig deep and unlock his spiritual powers. Ichigo's second-wind was accompanied with a massive increase in spiritual power, one which Zaraki soon found was just the sort of fight he had been waiting for. In the fight Ichigo would call on his sword's name and unlock it's ultimate power with it's bankai, a state all captains but Kenpachi had to unlock their full powers. With the aid of his bankia Ichigo was just barely able to fell Kenpachi. Yachiru saved her Captain shortly after the fight and instead of finishing off Ichigo is his weakened state choose to spare him so Kenpachi could have fun fighting him again. When Kenpachi awoke Yachiru told him she had spared him but not to consider it a defeat since she had to intervene to even the odds once Ichigo asked his sword for help. Kenpachi saw Yachiru's reasoning as an excuse and though he kept the title Kenpachi he would make fighting Ichigo again until one of them died his new goal in life.
After his full recovery Kenpachi would go on to help Ichigo and his friends survive the Soul Society's other Captains so that Ichigo could also recover and fight him again when he was done. Though events within the Soul Society and even Central 46 itself would eventually be revealed to be the machinations of a former Captain named Sōsuke Aizen. Ichigo and all his friends, Rukia included, would survive the ordeal. After the lengthy events most Captains considered reestablishing order and re-enforcing infrastructure to be their priority, however Kenpachi viewed fighting Ichigo as his top priority. Ichigo quickly left to avoid further conflict but Kenpachi viewed his rematch with Ichigo as an inevitability he would continue to look forward to. Since then Kenpachi Zaraki has considered Ichigo his most worthy opponent and willing to do anything to ensure his safety so that he could live to fight another day.
Powers and Abilities Accessories - Kenpachi attaches bells to his hair to alert his foes to his presence and wears a specially developed eye-patch that absorbs most of his Spiritual Power. He wears the bells and eye-patch so his opponents can last longer in a fight to give him a good show. Without his accessories Kenpachi can not control his speed and strength and will destroy a foe before they can even tell he is there. Kenpachi is the only Captain of the 13 Gotie with no bankai state. Kenpachi never learned to function on a spiritual level, in addition to being unable intentionally to limit his power output this means Kenpachi can not speak with the spirit of his sword and thus can not call it's name, which unleashes his bankai. Blood-lust - Kenpachi is renowned for his blood-lust. The need to shed blood is mainly what makes Kenpachi so dangerous as continued battle's don't weaken him, they just encourage him to fight harder and harder. Focus - Once Kenpachi sets his mind on a goal nothing can dissuade him. He is one of the few Soul Reapers who will openly refuse an order if it conflicts with his own wishes for battle. This single-minded focus is primarily what makes Kenpachi so hard to kill even when he is critically injured. Inspiration - Kenpachi is an inspiration to the entire 13 Gotie and Squad 11 in particular, who will fight harder than even they thought possible to live up to their Captain's high standards. Spiritual Aura - Kenpachi's spiritual aura is limited by his eye patch, but even so is so strong it can send shivers down his opponent's spines. Even with his eye-patch limiting his powers and no bankai, Kenpachi's aura is so strong it causes anyone not on-par with him to wound themselves with their own attacks as the force of each blow can not pierce his skin and instead reflects back on his opponents. Super Speed - Like most other Captains, Kenpachi Zaraki knows how to use flash-step, which allows him to arrive in a desired location so fast he seemingly appears out of thin air. Super Strength - Zaraki is one of if not the single strongest Soul Reaper, at least physically. Sword Mastery - Kenpachi Zaraki is considered the Soul Society's great sword master. Kenpachi prefers to use raw power behind each blow over style or form but was still required to learn Kendo in order to be declared a Captain. While he has never tested himself against the likes of Head Captain Yamamoto and he may no longer engage Retsu Unahana in combat he has otherwise proven his skill in one on one combat as the single greatest sword master in the 13 Gotie.