Father of Kohaku and Ruri. He was the village chief of Ishigami Village at the time of Senku's reawakening.

Spoiler

Kokuyo at first refuses to accept Senku as the new village chief, even though Senku won the Grand Bout. After witnessing Senku's antibiotic cure Ruri he officially crowns Senku the new leader of Ishigami Village. Despite not being the chief anymore, he serves as something of a co-leader of Ishigami Village, focusing on more practical concerns like food gathering, while Senku focuses on scientific advancement.