Nadeko is a childhood friend of Koyomi's sister and was cursed by a jealous classmates before being saved by Koyomi.
Nadeko is a character from the Monogatari franchise and has made appearances in the light novel series written by Nishio Ishin, featuring illustrations by Vofan, and published by Kodansha. She has also made appearances in the anime series based off of these light novels: Bakemonogatari and Nisemonogatari, both of which are produced by Shaft and published by Aniplex . Her original design is credited to the writer and illustrator of the light novel series while her anime appearance is credited to Akio Watanabe. She makes her first appearance in Bakemonogatari #9.
During grade school, a boy confessed his love for her and she rejected the confession, claiming she was in love with someone else. What she didn't know is that one of her classmates was in love with the boy who confessed. Jealous, the girl casts a curse on Nadeko that caused an invisible snake to envelope her body and slowly crush the life out of her. Upon finding out, Nadeko performs a ritual that requires her to kill a snake in a temple. However, this only made the curse worse. Eventually, Koyomi finds out about the curse and seeks Oshino for help; he tells him that they must perform the right ritual in the temple.
The ritual is successful and the invisible snake disappears, however, they soon find out that there was not only one, but two snakes crushing her body: one from the jealous girl and another from the boy who was rejecting. Koyomi takes the snake out of her body and saves her just in time.