Kiyomasa Kato appears in the film Azumi as a powerful warlord and a primary antagonist. He is depicted as a rebel head of the old Toyotomi force, making him a significant threat to the ruling Tokugawa shogunate. Serving as a key target for the protagonist and her fellow assassins, Kato is a formidable and cunning figure who has risen to a position of great influence. His role in the story is defined by his status as a high-value assassination target, and the mission to eliminate him is the central objective for the group of young warriors as they venture out from their secluded training valley.

In terms of personality and motivations, Kiyomasa Kato is portrayed as an infamous and ruthless warlord. His actions reveal a strategic and deceptive mind. Understanding that he is a marked man, he employs a clever and self-preserving tactic by having a double stand in his place at a critical moment, allowing him to survive an initial assassination attempt. This act demonstrates his shrewdness and his determination to hold onto his power by any means necessary. Rather than simply being a passive target, he is proactive in his cruelty, enlisting a group of counter-assassins to hunt down and eliminate Azumi and her comrades in retaliation for the attempt on his life. This sets in motion a deadly trap that ensnares the protagonists, leaving them with little room or time for doubt as they are forced to confront the brutal consequences of their mission.

While the provided information confirms his pivotal antagonistic role, details on his background, specific personal relationships with other characters besides his comrade who hires the counter-assassins, his internal development throughout the film, and any notable individual fighting abilities are not available. His primary function in the narrative is as a major obstacle and a representation of the corrupt power the young assassins have been trained to destroy.