|“||Ah, sheesh... Did I get stuck with a troublesome King, or what?||”|
According to Kisuke Urahara and Yoruichi Shihoin, Zangetsu is considered to be one of the most powerful Zanpakuto's in the Soul Society, as well as one of the original remaining Soul Blades from the aftermath of the Quincy Uprising.
Zangetsu appears to be virtually identical to Ichigo Kurosaki, except inverted in color. He is a fairly tall and lean-built being with white skin and hair. His eyes consist of black pupils, white irises, and black sclera. He has black nails. He also wears an inverted variation of the Soul Reaper uniform, as he wears a white shihakushō with a black cloth belt.
Zangetsu's most distinguishing features are his maniacal laughter and psychotic grins. He is brutal, arrogant, disrespectful, and sadistic. Zangetsu's reason for existence is to take over Ichigo's power and body and use it to kill everything and anything he sees, as opposed to Ichigo's desire to protect. Though he taunts Ichigo as being a weak and unsuitable counterpart of himself, he relishes the idea of Ichigo growing stronger as he also grows stronger as a result. Unlike Ichigo, he battles like a berserker, ignoring injuries and overpowering his enemies with brute strength and force. He protects Ichigo's body when he is about to die because if Ichigo dies, he will as well. Due to his status as a Zanpakutō spirit, Zangetsu doesn't get much opportunity to fight and gets really excited on the rare occasions he does get to fight. Zangetsu has declared Ichigo, and later Issei, is the "king" of the inner world, and he is the "horse". Zangetsu wishes to "take the crown" from Ichigo so he can have control over his body and become the dominant personality because he refuses to put up with Ichigo's softness of trying to defeat his enemies with reason and logic, which would eventually result on both him and Ichigo getting killed. After his loss, he states he is willing to allow Ichigo to keep the crown for now, but once Ichigo "screws up again", he will make his move once more. Zangetsu made good on this promise when Ichigo was nearly killed against Ulquiorra Cifer, at which point, he took control of Ichigo's body once again.
In regards to Issei, however, Zangetsu has mellowed out over the years. While he is still disrespectful and arrogant, he has grown to be more calm. While not interfering at first, he does give Issei advice, and quickly becomes more interested when he awakens to his Sacred Gear. When Issei has nearly been defeated by Riser, feeling his resolve to win, Zangetsu reveals his name to him out of mere interest after fighting him in his inner world. According to Urahara, Zangetsu recognizes Issei as his rightful master, even remarking that Issei, in spite of his perverted tendencies, reminds him of Ichigo.