In the live-action film Rurouni Kenshin Part I: Origins, Aritomo Yamagata is depicted as a high-ranking official in the Meiji government, serving as a general and a leader within the new Imperial Army. His character is grounded in his historical role as a key figure from the Chōshū domain who helped overthrow the Tokugawa shogunate and subsequently became an architect of modern Japan's military and political systems.

Yamagata is a tall man with light brown hair brushed back from his face, thin eyebrows, and a prominent handlebar mustache. His age is suggested by the wrinkles on his face, and he is almost always seen in a formal brown military uniform and matching cloak, projecting an image of authority and discipline.

His personality is defined by a fierce and unyielding dedication to the new government he helped to create. Having survived the violent turmoil of the Bakumatsu period and risen to the top of the ensuing power struggle, he is portrayed as highly intelligent, resourceful, and crafty. He views his own life as expendable in service to the peace and prosperity of Japan, a mindset that makes him a formidable and unwavering political operator. This devotion manifests as a pragmatic, sometimes relentless, approach to securing the nation's future, even if it means recruiting those who wish to leave their violent pasts behind.

Within the story of the film, Yamagata’s primary role is that of a former comrade to the protagonist, Himura Kenshin. They fought on the same side during the wars of the Bakumatsu, and Yamagata is aware of Kenshin’s legendary reputation as the hitokiri Battosai. Upon learning that Kenshin has reappeared in Tokyo, Yamagata seeks him out. His motivation is not one of punishment or justice, but of honor and utility. He offers Kenshin a high-ranking position as a general in the new Imperial Army, believing that a man of Kenshin's abilities should be rewarded and continue to serve the country he helped to build.

This offer creates the central conflict for Kenshin at that point in the story, as Kenshin has taken a solemn vow to never kill again and wishes only to protect the people around him as a wanderer, seeking no reward for the blood he has already shed. Yamagata’s persistence in this matter highlights the tension between the new Meiji government, which seeks to consolidate power by any means, and those like Kenshin who are trying to leave the revolutionary era behind. Their relationship is defined by this shared history and diverging paths; Yamagata represents the institutional call to duty, while Kenshin represents the personal choice of atonement.

The character does not undergo significant development within the film itself, serving more as a representative of the Meiji establishment. However, his background reveals a man who has evolved from a young revolutionary into a powerful statesman. In flashbacks, a younger version of Yamagata, then going by the name Kyosuke Yamagata, is shown to have held a less favorable opinion of Kenshin’s brutal efficiency as the Battosai. This suggests that his later desire to recruit Kenshin is a political calculation born from pragmatism rather than personal affection.

Regarding abilities, Yamagata’s primary strength is not as a warrior but as a political and military strategist. He is highly skilled in the way of governmental affairs, having risen to a position of immense power and control. His true talent lies in his ability to navigate the complex and dangerous landscape of Meiji politics, using his authority to command the army and make decisions that shape the nation's future. He is a master of statecraft, whose influence is felt through orders and policies rather than through direct combat.