Kotarou Katsura is a former Joui patriot and the leader of a moderate Joui faction who spends much of his time as a fugitive wanted by the authorities. He was one of the three students of Yoshida Shouyou alongside Gintoki Sakata and Shinsuke Takasugi, a shared history that forms the bedrock of his identity and motivations. Having fought in the Joui War, he initially resisted the Amanto takeover through violent means, but his methods and worldview gradually moderated as he grew to value the people of Edo and believe in change without unnecessary sacrifice. This conflict between his past violence and his present ideals defines much of his character.

In the events of Gintama: The Final Movie, Katsura steps into an unexpected role, briefly taking on the identity of Donald Zuramp and becoming the Prime Minister of Japan in order to influence the political landscape before the final confrontation. This act highlights his underappreciated strategic brilliance and his ability to operate on a grand scale when the situation demands it. Despite this high-level maneuvering, he never loses his signature eccentricity. He is notoriously proud of his name and refuses to be called anything else, especially Zura, a running gag that underscores his serious yet oddly sensitive nature. He is almost always accompanied by Elizabeth, a mysterious and inexplicable alien being whose silent presence perfectly complements Katsura's own brand of absurdity. His personality is a unique blend of deadpan seriousness, old-fashioned humor, and a penchant for dramatic storytelling that can move others to tears.

Katsura's role in the film's narrative is twofold. He provides a source of comedic relief, but more importantly, he acts as a vital tactical mind and a formidable combatant during the assault on the Terminal. He is tasked with holding onto the heart of Shouyou, a duty that places him at the center of the film's climactic conflict. His key relationships are deeply rooted in his past. With Gintoki Sakata, his bond is a mix of constant bickering and unwavering loyalty, a brotherhood forged in war and shared childhood mischief. His relationship with Shinsuke Takasugi is equally complex, evolving from bitter ideological opposition to desperate alliance for the sake of their teacher. Both relationships are central to the film's emotional core. Katsura himself voices this bond in the climax, stating over a radio that he spent his childhood covering for Gintoki and Takasugi and refuses to stop now, a simple but profound statement that defines his place in the trio as the responsible but equally loyal cornerstone.

Throughout the film, Katsura undergoes a significant transition. He moves fully from a revolutionary hiding in the shadows to a legitimate leader who helps stabilize the country after the final conflict. He survives the events and seeks out the remnants of the Kiheitai, symbolizing a future where old wounds might heal. His development culminates in his acceptance of his role not just as a rebel, but as a protector of his friends and their shared legacy. In terms of abilities, Katsura is a master strategist, a highly skilled swordsman, and an expert in the use of explosives. He is also deeply proficient in the arts of disguise and escape, skills honed during his long years as a fugitive. His tactical insight and unparalleled knowledge of his former comrades make him an indispensable asset in the final battle against the Tendoushuu and Utsuro.