Nurarihyon is Rikuo's grandfather, known as the master of all spirits or as the Supreme Commander. It is said that he plays pranks and hates humans, but he doesn't really hate them - rather, he doesn't believe humans should interfere in yōkai affairs. He dislikes the fact that Rikuo goes to school and acts human but respects his wishes.
400 years ago, he fell in love with Yōhime and fought with the Hagoromo-Gitsune in Kyoto for Hagoromo-Gitsune kidnapped Yōhime to eat her liver.. At first things looked grim for Nurarihyon, but when Hagoromo-Gitsune mocked him, Nurarihyon finally was able to slash Hagoromo-Gitsune's current body host, saving Yōhime. But Hagoromo survived the slash and fled to the roof where Nurarihyon followed her. They then clashed again for the second time, this time on the roof with both being equally matched. It was only when Keikain Hidemoto arrived and tip the balance of scales in favor of Nurarihyon by helping Nurarihyon battle Hagoromo-Gitsune. Both defeated Hagoromo-Gitsune but before the host Hagoromo-Gitsune was residing in, she was able to puncture through Nurarihyon and took his heart and consumed it to restore a bit of her strength which left a gaping hole in Nurarihyon's chest and caused Nurarihyon's life span to decrease. When Nurarihyon was In his prime, he and Keikain Hidemoto were considered friends. Even in his old age, he can easily best "Night" Rikuo and Muchi. Normal demons feel so much "Fear" that he is invisible to them until he strikes, that is his "Meikyō Shisui".

He is still able to appear in this form, as shown in an episode from "Demon Capital", despite his old age/normal appearance that he usually appears in as Rikuo's grandfather.