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


Kokuyo is a large man, with a big beard and a ponytail.


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 he didn't care for Ruri's well being. However, he does care for Ruri as he worries for her health. He is wary of outsiders especially Senku but later grows to accept him and states making him leader was not a mistake. 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 Senku brought was for throwing at enemies and not realizing he was going to use it for an experiment. Ruri and Kohaku claim this is because he came from the older generation. 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 anticipates her to reject. He is saddened when she shows no sentiment towards the shield and quickly uses it in the invention.

Abilities and Skills



Kingdom of Science Arc

Village Games Arc


  • 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.


Site Navigation

v  e
Post Petrification Humans
Male ChromeGinroJasperKasekiKokuyoKinroMagmaSoyuzTetsuken
Female GarnetKohakuRubyRuriSapphireSuikaShiroganeTurquoise
Community content is available under CC-BY-SA unless otherwise noted.