Nadeko, the main character of Nadeko Snake, is Tsukihi’s friend back in elementary school. She always wears a waist pouch, always casts her eyes downward, has her bangs covering her eyes, has a shy personality, and can be easily amused. Koyomi played with her a lot whenever she visited his house after being invited by his sisters. She was put under a curse by a classmate where an invisible snake would strangle her and was going to die until Koyomi found out and offered her his help. It was revealed that there were two snakes strangling Nadeko. One is placed by the girl who was in love with the boy Nadeko rejected, and the other was placed by the boy Nadeko rejected. Koyomi managed to get rid of the first one but was unable to do so with the second one. The snake then returned to the boy who cursed her and cursing him instead. She refers to Koyomi as Koyomi-onii-chan. She's quite protective of her hair (particularly her forelocks) thinking that it's her place to guard more than her panties. When she finally combed her forelocks aside in Nisemonogatari, Koyomi commented that she has a glare just like a serpent.
In Nadeko Medusa, during Halloween, Nadeko met a girl named Ōgi, and after which she was able to see a white snake who claimed to be one of the snakes she killed during the events in "Nadeko Snake", pressuring her to atone for what she caused by finding the remains of the snake when it was alive. In the official guidebook, Nisio Isin did an interview with all of the voice actors, and asked Kana Hanazawa on what character she would like to play, in which Kana Hanazawa replied that she'd like to play an evil character, probably becoming the basis of Nadeko Medusa. It seems Hitagi and Shinobu both dislike Nadeko.
