Yaichirou Shimogamo is the eldest son of the Kyoto-based Shimogamo tanuki family. Driven to become the Nise-emon, the leader of tanuki society, he strives to uphold the legacy of his late father, Souichiro Shimogamo, a position carrying immense responsibility despite his family's challenges. He embodies a strong sense of duty and responsibility as the first son, fiercely protective of his younger brothers, especially shielding Yashiro from bullying by their Ebisugawa cousins, Kinkaku and Ginkaku. However, Yaichirou possesses a short temper, reacting emotionally and often lashing out violently or undergoing dramatic transformations when provoked. His volatility erupts physically through shapeshifting into a large tiger during moments of high stress or confrontation. Yaichirou's path is deeply shaken upon discovering that his brother Yajiro inadvertently played a role in Souichiro's capture by the Friday Fellows. This revelation shatters his ideals and forces him to grapple with complex feelings of betrayal and grief. Despite this turmoil, his core commitment to his family and his ambition to become Nise-emon remain driving forces. His mother, Tousen, maintains pride in him even as broader tanuki society dismisses the Shimogamo brothers. His relationship with the rival Ebisugawa family, particularly his uncle Soun Ebisugawa, is adversarial. Soun, who betrayed Souichiro out of envy over losing the Nise-emon position and the love of Yasaburo's mother, actively undermines Yaichirou's ambitions. This conflict fuels the central familial and political tensions within the tanuki world.