A race of yokai that inhabit Zipangu. Often deliberately evasive during conversations just to tease people, they have unconventional personalities that are slippery and hard to grasp; and are said to set foot inside people's houses unnoticed and begin to make themselves at home as if it were their own house, sipping tea and smoking a kiseru. At a glance, this race is nearly human in appearance, but they are among the most distinguished of the great yokai of Zipangu and are said to drape their body in the darkness of night and command one hundred demons. Night is the time of the yokai, and just by being there, the nurarihyon who drape themselves in the darkness of night invigorate the yokai, creating a passionate nighttime atmosphere for married couples.
After entering the home of a man she's taken a liking to, she'll treat the home owner in a relaxed, friendly manner, and even dine with him, but it's said that the occupants of the home will be unable to sense that anything is amiss, as if they were seized by the delusion that the nurarihyon herself is the mistress of the house. And, as if it were only natural, she'll also enter the man's bed; but even so, the man won't be able to feel that there’s anything odd about her being there sleeping with him in his futon. On the contrary, he'll feel that it's a natural thing to be embraced by her since she is the mistress, and he'll even feel delighted to have been chosen as her partner.
As rulers of the night, they are also temptresses who possess superior seduction techniques, and just by stroking with their slender fingertips, they can provide a man with comfortable pleasure. In fact, it's said they can even cause a man to ejaculate at will with only a single fingertip. If one were to spend a night with a nurarihyon, the pleasure would be so overwhelming that even reality would then feel hollow, and ruminating on the deed would only cause him to miss them more. A man would just feel inextricably compelled to wait for the yokai to visit again the following night.
Even after that, the nurarihyon would continue to stay in the man's house, but since they joke around all the time, it's impossible to grasp their true feelings, so sometimes men may experience feelings of loneliness and anxiety when unable to tell for certain whether the nurarihyon like them. However, the words of love they whispered at night in bed don't give off the usual joking vibe at all, and they definitely convey their true feelings. For that reason, men will start to long for the arrival of the night from the bottom of their heart.
As rulers of the night, they possess an enigmatic charm that is both fascinating and majestic. Their appearance inspires yearning not only in yokai, but in humans as well. In the case of a man, he'll experience a powerful attraction to yokai and desire to become a yokai's partner. In the case of a woman, she'll end up desiring to become a yokai herself just like them.
It is also said that men who become their husbands have a charm that is so attractive to yokai that they were chosen as their partners. By copulating with them every night and coming to desire perpetual night, that charm will eventually be made to bloom, and a man will become a worthy ruler of the night who can stand alongside the nurarihyon as her equal. He'll become someone who can dominate many yokai with his body, a being worthy of serving. Many yokai will be attracted to the man and desire to spend the night with him as his concubines. Due to the nurarihyon being draped in the darkness of night, the man's surroundings will be altered into a state of perpetual night with yokai always seeking copulation. As their master, he will end up spending the never-ending night copulating with yokai one after another. It will reach the point that at any given time, the man will always have a crowd of yokai who yearn for him surrounding him, and if the man were to take a walk outside, the yokai following after him would form a huge swarm, creating a spectacle known as “a night parade of one hundred demons".
- TL Note 1: Yobai (夜這い?, "Night crawling") is an ancient Japanese custom that was usually practiced by young unmarried men and women. It was once common all over Japan and was practiced in some rural areas until the beginning of the Meiji period and even into the 20th century. At night, young unmarried men would silently enter houses with young unmarried women. A man would silently crawl into a woman's room and make his intentions known. If the woman consented, they would sleep together. By the morning he would leave. The girl's family might know about it, but pretended they did not. It was common for young people to find a husband/wife like this.
- TL Note 2: Kiseru (煙管 kiseru?) is a Japanese smoking pipe traditionally used for smoking kizami, a finely shredded tobacco product resembling hair. Notably they were sometimes modified to double as weapons, since they were basically rods with metal ends.