Kokuyo, a muscular middle-aged man, sports blond hair tied in a ponytail and a long brown beard, his weathered face marked by thick brows and piercing brown eyes. He dons a blue robe over a white undercloth, a rope coiled around his neck. As Ishigami Village’s former chief, he enforces strict pragmatism and security, exuding a gruff authoritarianism. This drives him to disown his daughter Kohaku for challenging village norms—preventing Magma’s rise to chiefdom and her sister Ruri’s forced marriage—while covertly preparing her to inherit Ruri’s priestess role, fearing Ruri’s chronic illness. Having earned leadership through combat in the village tournament, Kokuyo values physical prowess and tradition. He initially resists outsider influence, distrusting Senku’s scientific approaches until antibiotics cure Ruri’s pneumonia. This pivotal moment compels him to cede authority to Senku, though he remains a revered co-leader, mobilizing defenses against threats like Hyoga’s forces with katanas forged by Senku’s team. His rigid worldview softens as science proves its worth, transitioning from misinterpreting tungsten as a weapon to applauding the Kingdom of Science’s innovations. Reconciliation with Kohaku follows her unwavering protection of Ruri and the village, though her pragmatic disposal of a shield he gifted her exposes his hidden longing for familial bonds. In the Stone Wars, Kokuyo strategizes defenses with paper shields and aids in repelling Tsukasa’s empire, later joining the Treasure Island expedition where he suffers temporary petrification. Revived, he resumes governance, overseeing drills and fortifications. His past—marriage to a priestess lost to illness and raising Ruri and Kohaku under strict traditions—fuels his initial resistance to change, yet his journey reflects a growing balance between heritage and progress.