This article contains details from the Thousand-Year Blood War Arc that have not yet appeared in the Anime.
Zaraki Kenpachi is the Captain of the 11th Division in the Goetei 13 and is one of the most powerful Shinigami in Bleach. What is even more impressive is that Kenpachi's powers have reached such epic proportions without the use of his Bankai, as the Soul Reaper has yet to learn its name.
This Captain is so OP that he wears an energy-suppressing eye patch during combat in order to even out the competition and rarely relies on other Shinigami or his second-in-command, Yachiru Kusajishi, for any assistance. He is a one-man army who wants nothing more than to find a worthy opponent, and surprisingly, Retsu Unohana steps (back) into those shoes.
The Thousand-Year Blood War Arc
During the Quincy Blood War, Zenpachi decides that he needs to step it up a notch and begins training with Unohana to try and unlock a greater power potential. The 4th Division Captain is one of the few fighters that Kenpachi respects, as she initially unleashed his passion for combat when they first crossed swords many years ago. As their training begins, Unohana appears to have the upper hand, even though Zaraki is fighting without his eye patch (at full power), and she lands several potentially fatal blows. However, Unohana used her healing powers to ensure Kenpachi is kept alive as she continues to push him to the limits. She believes that Zaraki grows stronger each time he returns from the brink of death and that this brutal combat style would be the only way to get Zaraki to break through the limitations he has placed upon himself.
Zaraki possesses a certain level of fear of his powers, as he is uncertain of how much death and destruction he could cause if he lets loose. It's as if he puts as much focus on suppressing his power as he does on finding a worthy opponent, an oxymoron that is surely causing internal conflict. Zaraki may have had a point though, as tragically, Unohana lost her life while training her comrade; although she dies with a smile on her face, knowing what she has achieved. Following her last breath, Kenpachi hears a voice for the first time, which is emanating from his Zanupakto.
Zaraki Kenpachi's Bankai Revealed
Viewers initially witness Kenpachi's Bankai, which he calls Nozarashi, during a match-up with the Quincy, Gremmy, not long after Unohana's demise. Gremmy has created a meteorite with his unique abilities and directed it towards Seireitei, but Zaraki leaps up and releases his Bankai, obliterating the collosal target with a single thrust. When Kenpachi's Bankai is released, the Soul Reapers' skin turns red and his Zanupakto transforms into an oversized scythe-ax-shaped blade, making this Captain look more hardcore than ever!
Similarily to Deku from My Hero Academia, Kenpachi will now have to focus on physical training to ensure that his body is strong enough to wield such extensive power. When the fierce Shinigami called on Nozarashi in his battle against Gerard Valkyrie, Zaraki's strike was so forceful that his own arm was blown away in the process, oops! However, with his new power, the Shinigami's Zanpakuto seems capable of slicing through absolutely anything, even the seemingly undefeatable Gerard, cleaving him cleanly in two.
The Consequences of Unohana's Death
Although it is the Captain's name, the word 'Kenpachi' also refers to a title, which is bestowed only upon the strongest Shinigami of Sereitei, and only one may claim that privilege in each generation. Surprisingly, the 'Kenpachi' from the Agent of the Shinigami arc was not the Captain-Commander, Yamamoto, but rather Uhohana. Because Zaraki was the one to kill her, he inherited the honors of being Kenpachi 'Kenpachi' (tee hee!)
However, as Unohana's life drew to an abrupt end, her words suggest that she had always planned on passing the title over to him, as she realized many years ago during their very first skirmish that Zaraki was worthy of such distinction. There seems to be no reason as to why Unohana could not heal her own wounds before dying, implying that she was sacrificing herself in order to help her friend succeed, while Zaraki begged Unohana to save herself.
It is highly unlikely that Zaraki will use his newfound status of officially being the strongest Shinigami to attempt to take the role of Captain-Commander and leader of the Gotei 13. He is not a man with the patience for admin and politics, and the added responsibility of being the ultimate leader does not appeal to his character. Heading the 11th Division is enough work for him because, at the end of the day, combat, and Yachiru, are the only things that make Kenpachi happy in Bleach.