Kokuyo is the father of Kohaku and Ruri, and was the previous chief of Ishigami Village before Senku.

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.


Kokuyo is a is a muscular man with blonde hair tied into a ponytail, he has a beard that does not match his hair colour that which it being brown, He wears a blue robe with a white under cloth with a rope tied around his neck.


Initially, he is a harsh man who disowns Kohaku as his daughter for constantly going against him, such as entering the village tournament and winning to prevent Magma from becoming the new chief and marrying Ruri. He also didn't seem to mind Magma being the new chief, despite knowing that he didn't care for Ruri's well being. However, he does care for Ruri, as he worries for her health. He seems to want to become closer to his daughters and becomes saddened when they don't reciprocate. For example, he gave Kohaku her shield and when Senku suggested using it in one of his inventions, he shyly remarks that he is fine with it as long as Kohaku is, but clearly expects her to reject. He is saddened when she shows no sentiment towards the shield and quickly uses it in the invention. He seems to later reconcile with Kohaku, as he realizes how hard she worked carrying water for her sister every day to delay her illness.

He is wary of outsiders, especially Senku, but later grows to accept him and states that making him the leader was not a mistake.

He can be rather simpleminded, believing the tungsten that Senku brought was for throwing at enemies and not realizing that he was going to use it for an experiment. Ruri and Kohaku claim this is because he came from the older generation.

Abilities and Skills

Physical Abilities

Kokuyo is one of the primary fighters of Ishigami Village, and won his generation’s Village Games. He was entrusted with a katana by Senku when it came time to repel Hyoga’s second attack on the village.


He won one of the previous village games and became chief. In commemoration of his victory, Kaseki made a shield for him. Some years later, he would pass the shield on to Kohaku. Ruri was stricken with pneumonia at some point in the past, and he began to make plans for Kohaku to learn the Hundred Tales and succeed Ruri as priestess in the event of her death. Kohaku refused to go along with this plan, creating a rift between Kokuyo and Kohaku that would continue into the present.


Kingdom of Science Arc

Village Games Arc

He declares Senku the winner of the village games and reveals the name of the village to be Ishigami Village, which is also Senku's last name.

Vs. Hyoga Arc

He defends the village with the katanas that Senku, Chrome, and Kaseki make.

He attempts to fight Homura after she sets the village on fire, but she escapes.

He leads the evac efforts for the village, as it burns down. Kokuyo later congratulates Suika on leading the enemy away and tells the village, they won the first battle in the war.

Communications Arc

When Senku makes electricity, Kokuyo is in awe at tasting cotton candy.

After Senku declare the age of energy, Kokuyo celebrates that the villagers can focus more on food and material gathering.

He is later seen when Senku plays the record his father left, being amazed to hear the village founder. Kokuyo remarks to himself that Kohaku is cold to him like Senku after she calls his treatment of his father cold.

Treasure Island Arc

He is upset after Soyuz revealed the truth about himself and his past.


  • His name contains the kanji for Black ( Kuro) and Jewel (曜石 Youseki) and, put together, mean Obsidian (Kokuyouseki), in keeping with the fact that all other members of Ishigami village have names referencing metals and crystals.


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