Kokuyo is the father of Kohaku and Ruri and served as Ishigami Village's chief prior to Senku's arrival. Though no longer chief, he acts as a co-leader, managing practical tasks like food gathering while Senku focuses on science. He is a large, muscular middle-aged man with blond hair tied in a ponytail, a long brown beard, gruff features, thick eyebrows, a large nose, and intense brown eyes. He typically wears a blue robe over a white undercloth secured by a rope. Initially harsh, Kokuyo threatened to disown Kohaku for breaking rules, such as entering the village tournament to stop Magma or bringing outsiders like Senku in. He remained indifferent to Magma potentially becoming chief despite Magma's disregard for Ruri's health. However, deep concern for his daughters surfaces in his worry over Ruri's illness. He longs for closer bonds with them, feeling sadness when Kohaku readily donated the shield he gave her as a memento for Senku's inventions, revealing his unspoken hopes for familial connection. He reconciled with Kohaku after witnessing her dedication to carrying water daily to delay Ruri's illness. Wary of outsiders, Kokuyo initially opposed Senku's rise to leadership. He accused Senku of sorcery during Ruri's treatment and attacked him when her condition worsened temporarily. After Ruri's full recovery, he acknowledged Senku's effectiveness, formally crowned him chief, and later affirmed that appointing Senku was not a mistake. He grows to appreciate the Kingdom of Science's innovations and comforts, praising Senku for adding fun to survival. His practical mindset sometimes leads to misunderstandings, like assuming tungsten was for throwing at enemies instead of science—a trait his daughters attribute to his generational perspective. Kokuyo possesses great strength as one of the village's primary fighters and winner of his generation's Grand Bout. He demonstrates swordsmanship, using katanas to defend against Hyoga's attack and in assaults on the miracle cave. His leadership experience commands respect; villagers follow his orders during crises, like evacuating seniors and children when Homura threatened the village. Historically, he won a village tournament to become chief, commemorated by a shield crafted by Kaseki, which he passed to Kohaku. When Ruri contracted pneumonia, he planned for Kohaku to learn the Hundred Tales and become priestess, creating a rift when she refused. Throughout key arcs, Kokuyo's role evolves: - In the Village Games, he opposed Senku's participation and rejected him as chief after his victory. He blamed Senku for Ruri's worsening condition during treatment but accepted his leadership after her recovery. - During the Vs. Hyoga arc, he stopped Kohaku from a dangerous fight and led village defenses with katanas. He was defeated due to Gen's sabotage and coordinated evacuations when Homura set the village ablaze. - In the Communications arc, he enjoyed inventions like cotton candy but misunderstood Senku's intentions, assuming jewels and tungsten were for defense. He felt sadness when Kohaku showed no attachment to the gifted shield. - On Treasure Island, he traveled on the Perseus, expressed anger at the Why-man, and was petrified twice—first by Kirisame, then by Ibara—before being revived both times. - During the South America arc, he witnessed the global petrification beam and ordered villagers into defensive positions before being petrified. - Nine years later in the Globetrotting arc, he was revived by the returning Kingdom of Science. He expressed joy at Kohaku's return and clarified neither he nor the villagers built the protective wall shielding them during petrification. Kokuyo transitions from rigid traditionalism to accepting scientific progress and Senku's leadership, motivated by his daughters' well-being and the tangible benefits science brings the village.