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 large muscular man with blonde hair tied into a ponytail, he has a beard that does not match his hair color 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 threatens with disowning 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 or bringing an unknown figure to the village. 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 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. Despite his practical and initially simple view of the world, he develops an appreciation for the comforts that the Kingdom of Science has brought his village and its people. He praises Senku for not only being an effective leader and worthy successor, but someone who has brought out a crucial element for survival: fun.
Abilities and Skills
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 is also coordinated and strong enough to slowly pour a great amount of molten glass into a lens.
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.
With Senku's arrival to the village, Kokyuo is appalled by Kohaku's disobedience. Angered, he says he might eventually disown her given how she constantly breaks village's rules.
After Senku, Chrome, Kohaku and Suika make ramen and goad some villagers into trying it, Kokuyo is becoming more and more concerned for the village. Jasper asks Kokuyo whether or not they should go out to eat themselves, which Kokuyo rebukes. The former gets elbowed by his wife for making such a suggestion, as Ruri gets worried about what Kohaku's business with an unknown figure is.
Kokuyo compliments the weather on the day of the tournament, and asks Turquoise whether the preparations are set. When Turquoise berates her husband for allowing Kohaku into the fight, Kokuyo states that it's fine - he wouldn't let a village chief be someone who can't beat a woman. Jasper then informs Kokuyo that Senku has also joined the village games.
When Ruri approaches Senku to inquire him about his surname, she collapses from her ailment. Kokuyo rushes towards his daughter, scolding Jasper for letting her walk while feeling sick.
He comments on Senku's cunning nature as the latter uses an unorthodox technique with his spear to hit Ginro in the groin. Soon after, Senku wins by Chrome getting disqualified from fainting and becomes the village chief. An angry Kokuyo states that he won't accept an outsider like Senku as the village chief, only to be rebuked by Senku who calls him a former village chief and says he has no interest in what a former figure of authority has to say. Once Senku acquires alcohol for the antibiotic formula, he immediately divorces Ruri and drags Kohaku and Kaseki away with him, further shocking the former village chief who orders Senku to be caught but is stopped by Kinro who vouches for the mysterious scientist. Once the cure is finished, an uneasy Kokuyo observes Ruri taking a suspicious drug for her illness.
Once Ruri's condition worsens, Kokuyo blames Senku who fed the drugs to her beforehand. Senku confirms this, however he states that the reason behind the more critical condition is because bacteria in question is mobilizing forces as its existence is threatened. Kokuyo goes on to call it sorcery, still angry and attempting to attack him. His attack is stopped by Kohaku who states she believes in Senku, while the rest of the group also nods in unison. After continuous consumption of the drug, Ruri is finally able to walk normally again, having been cured of the ailment. Kokuyo and his other daughter cry tears of happiness, seeing their relative finally well again. The former chief officially crowns Senku the new leader of the Ishigami Village.
Kokuyo later defends the village from Hyoga and his men with the katanas that Senku, Chrome, and Kaseki make. Kokuyo and the rest of the warriors are quickly dispatched by Hyoga, whose spear breaks upon exerting too much force - thanks to Gen tampering with it prior to the second invasion.
Kokuyo 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 celebrates with the village their win over the first battle in the war.
Once the cotton candy machine is crafted as a part of the cellphone making process, Kokuyo enjoys the taste of the sweet along with the rest of the villagers.
While discussing the problem of manpower in preparation of the cellphone, Kokuyo mentions that a portion of people needs to be delegated to ready the village for the winter. As Senku comes up with an idea of utilizing gears to ease the burden on the working force, Kokuyo is shocked to see that Kohaku readily gives up her shield which he gave her as a memento of the past to be used as a gear itself.
Kokuyo is amazed by a method to preserve meat over winter by bottling the food in a glass pots.
He is later seen when Senku plays the record his father left him, being amazed to hear the village founder. Kokuyo sadly remarks to himself that Kohaku is cold to him like Senku after she calls his treatment of his father cold.
He travels on the Perseus to gather a way of creating more revival formula. During the voyage, is upset after Soyuz revealed the truth about himself and his past. However, he relents after realizing how hard it was for him.
He is petrified by Kirisame but gets revived by Senku.
Kokuyo is petrified once again, because of Ibara's last resort.
Kokuyo bears witness to the training of his daughter and Kirisame, remarking on their skill.
Kokuyo journeys with his allies to America.
He is later overjoyed at enjoying ice cream.
- His name contains the kanji for Black (黒 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.
|Male||Chrome • Ginro • Jasper • Kaseki • Kokuyo • Kinro • Magma • Mantle • Soyuz • Tetsuken • Ibara • Mozu • Oarashi • Matsukaze|
|Female||Garnet • Kohaku • Ruby • Ruri • Sapphire • Suika • Shirogane • Shovel • Turquoise • Amaryllis • Kirisame|
|Male||Taiju Oki • Senku Ishigami • Gen Asagiri • Chrome • Kaseki • Kinro • Ginro • Magma • Kokuyo • Ryusui Nanami • Matsukaze • Tsukasa Shishio • Hyoga • Mozu|
|Female||Yuzuriha Ogawa • Ruri • Kohaku • Suika • Nikki Hanada • Minami Hokutozai • Kirisame • Homura Momiji|