From the Bleach Universe:
* Aizen Sousuke: Aizen possesses overwhelming power and the ability to manipulate the flow of spiritual energy, making him a formidable opponent. He could potentially exploit Kenpachi's reckless fighting style and use his abilities to gain the upper hand.
* Ichigo Kurosaki (Full Hollowfication): Ichigo in his full Hollowfication state is incredibly powerful and possesses abilities that could challenge Kenpachi. His immense spiritual pressure and raw power could potentially overwhelm Kenpachi.
* Yhwach: Yhwach, the Quincy king, is one of the strongest characters in the Bleach universe. He possesses immense power and the ability to manipulate the flow of spiritual energy, potentially giving him an advantage over Kenpachi.
* Yamamoto Genryūsai Shigekuni: As the former Captain Commander, Yamamoto is a highly skilled and powerful swordsman. His Bankai, Ryujin Jakka, is incredibly destructive and could potentially overpower Kenpachi.
* Kisuke Urahara: While not a direct combatant, Urahara's genius intellect and tactical abilities could potentially allow him to find a way to defeat Kenpachi. He could potentially use his knowledge of Kenpachi's fighting style and abilities to create a strategy to exploit his weaknesses.
From Other Universes:
* Goku (Dragon Ball): Goku, from the Dragon Ball universe, is known for his incredible power and relentless training. He could potentially outclass Kenpachi in terms of raw power and speed.
* Naruto Uzumaki (Naruto): Naruto, with his immense chakra reserves and powerful jutsu, could potentially challenge Kenpachi. His ability to manipulate chakra and utilize powerful techniques could potentially give him an edge.
* Saitama (One Punch Man): Saitama is known for his overwhelming power and ability to defeat opponents with a single punch. While Kenpachi is incredibly strong, Saitama's sheer power could be a significant factor in a fight.
Key Factors in Determining a Winner:
* Fighting style and strategy: Kenpachi's reckless fighting style can be both his strength and weakness. A more strategic and cunning opponent could potentially exploit his weaknesses.
* Spiritual pressure and abilities: Kenpachi's immense spiritual pressure and Zanpakuto abilities are formidable, but opponents with similar or greater power and abilities could challenge him.
* The context of the fight: The specific circumstances of a fight, such as the environment and the availability of resources, can have a significant impact on the outcome.
Ultimately, who can defeat Kenpachi is a matter of speculation and depends on the specific matchup and the circumstances of the fight. While Kenpachi is incredibly powerful, there are many characters who could potentially challenge him and potentially emerge victorious.