Hyakushūbō is a supporting character in the Beast Kingdom, serving as a calm and reasonable presence amidst the often chaotic lives of the main characters. He is a monk with the physical appearance of a humanoid pig, possessing a build similar to an average human but with distinctly porcine facial features. His role within the story is primarily that of a grounded advisor and a voice of reason, often tempering the fiery and abrasive personality of the warrior Kumatetsu.

As a monk, Hyakushūbō embodies patience, neutrality, and a collected demeanor, which provides a stark contrast to the hot-blooded nature of his friend Kumatetsu. He is frequently seen alongside Tatara, another of Kumatetsu's acquaintances, and together they form a support system for the protagonist, Kyuta. Unlike Tatara's more laid-back and sometimes cynical attitude, Hyakushūbō maintains a tranquil and thoughtful disposition, offering perspective and guidance during difficult situations. Throughout the film, he functions as part of the "village" that helps raise and advise the young boy, contributing to his emotional and moral development. In a narrative examining different forms of fatherhood and mentorship, Hyakushūbō represents a calm, uncle-like figure whose wisdom helps the main characters navigate their personal struggles. His consistent presence serves to explain the significance of certain events and the growth of the protagonists, helping to clarify the film's themes of family and perseverance. Beyond his advisory role, he also participates in key journeys, such as traveling with Kumatetsu and Kyuta to meet the various lords of the beast world, providing both logistical and moral support for their quest. His designated role as a monk aligns with his function as a moral compass, and he is established from the beginning of the story as an individual who tempers Kumatetsu's impulsiveness with his own measured and reasonable approach to conflict and teaching.