Bunchou serves as the film's primary antagonist, initially appearing as Mamoru Shizime, the newly elected mayor of Kasukabe championing ecology. He secretly leads the organization "Save Keeping Beautiful Earth" (SKBE) and masterminds the "Human Animalization Plan." This initiative employs a specially developed green liquid formula to transform humans into animals, aiming to halt environmental destruction by erasing human memories and instincts. Bunchou believes humanity's disregard for nature necessitates these extreme measures.
His motivations arise from witnessing widespread environmental neglect and deep personal despair, intensified by his wife Yoshiko Shizime's perceived indifference to ecological issues. Yoshiko operates as Victoria within the story. Consumption of the green liquid causes complete physical transformation into animals, as seen with Hiroshi Nohara becoming a rooster and Misae Nohara a leopardess. Partial consumption results in hybrid forms retaining human heads, like Shinnosuke's friends.
As the plan unfolds, Bunchou directs subordinates, including Bunbetsu, to capture transformed individuals. His confrontation with the Nohara family escalates at SKBE's underground forest base. During the climax, Bunchou consumes an enhanced "DX" version of his formula, transforming into a powerful chimera hybrid to physically overwhelm his opponents. The resolution comes when Yoshiko/Victoria intervenes, reveals her identity, and confronts him about their fractured relationship. This prompts Bunchou to abandon his plan, destroy the remaining formula to prevent her consumption, and reconcile with her. He apologizes and relinquishes his mission.
The transformation effects reverse for all affected individuals following Bunchou's surrender. His character arc concludes with a renewed emphasis on environmental consciousness, notably influencing Hiroshi Nohara's heightened ecological awareness. Bunchou's background as a disillusioned environmentalist and his personal reconciliation with Yoshiko form the core of his narrative role.