Kokuyo held the position of chief in Ishigami Village before Senku's arrival, commanding authority and respect. He is the father of Kohaku and Ruri; his wife, the previous village priestess, passed away. Following her death, Kokuyo expected Ruri to become priestess. When Ruri fell severely ill, he attempted to force Kohaku into the role instead. This choice sparked significant tension with Kohaku, who resisted village traditions, worsening when she defied his wishes to win the martial arts tournament—leading him to temporarily disown her. He possesses a strong, muscular physique characterized by blond hair tied in a ponytail, a long brown beard, and intense brown eyes. Kokuyo typically wears traditional village attire: a blue robe over a white undercloth secured by a rope, reflecting his warrior and leadership background. His personality blends strict rule adherence with underlying sentimentality. As chief, he enforced traditions rigorously, manifesting in harsh treatment of Kohaku's disobedience. He expressed disappointment when she readily allowed Senku to repurpose a commemorative shield he gifted her, revealing his attachment to meaningful objects. Despite his stern exterior, he demonstrated care for his daughters, particularly worrying about Ruri's health. Initial distrust of outsiders like Senku transformed into respect after witnessing scientific solutions to village problems. Kokuyo acknowledged past mistakes regarding his daughters and came to appreciate the improvements Senku brought, including life-enhancing technological advancements during winter. A former champion of the village martial arts tournament, Kokuyo maintained formidable combat abilities, ranking among the village's strongest. He skillfully wielded weapons, including a katana during Hyoga's invasion. His leadership persisted beyond his formal tenure, with villagers following his directives during emergencies like the village attack and evacuation. Kokuyo actively participated in key village affairs post-chiefship. He opposed Senku's initial rise to leadership but formally recognized him after Senku cured Ruri's pneumonia. During Hyoga's attack, he helped organize the defense using katanas crafted by Senku's team. He later joined the voyage on the Perseus to Treasure Island for revival materials. On this expedition, he was petrified twice—first by Kirisame, later by Ibara—and revived both times. He remained in Ishigami Village as a leader while others undertook global missions. During the second worldwide petrification event, he instructed villagers to assume protective positions before being petrified. Revived nearly a decade later, he expressed joy reuniting with returning Kingdom of Science members. His relationships evolved significantly: his bond with Kohaku improved as he recognized her dedication to helping Ruri and acknowledged her strength; with Ruri, he maintained a protective, caring dynamic focused on her health. Initial distrust of Senku turned to respect after Ruri's cure, leading him to value Senku's leadership. Kokuyo maintained a cautious but non-interfering stance toward Chrome's activities with Senku and Kohaku. After Soyuz revealed his identity as an astronaut's descendant, Kokuyo initially reacted with anger but forgave him after hearing his full story.