Guts is the protagonist of the story. A tall, muscular male with a huge sword called the Dragon Slayer, a prosthetic left forearm that has a magnetic grip, and also conceals a cannon. Guts is a tragic hero; he is born as one who may be able to struggle against Causality, but seemingly unable to affect it on a large scale.

Zaraki's surname comes from the district he once resided in, Zaraki, which is district #80 of the North Alley of Rukongai. District #80 is the worst, most lawless region of Rukongai, full of thieves and murderers (whereas area #1 is the most orderly and law-abiding). While residing in District #80, Kenpachi was nameless. During that time, he became proficient in swordsmanship and killed numerous enemies.
After some time had passed, Kenpachi found his way to the Seireitei. He defeated and killed the previous Captain of the 11th Division (whose identity is currently unknown) and gained his seat in the Gotei 13 in this manner.