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 refers to Koyomi as Koyomi onii-chan and appears to have feelings for him.
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, probably foreshadowing the story of Nadeko Medusa.
She was cursed two times by a classmate who liked the boy she rejected, and the rejected boy. While the first one is banished, Koyomi is forced to battle the second to keep it from killing Nadeko.
During Halloween, Nadeko met a girl named Ougi who gave her a white scrunchie. After, she was able to see a white serpent, Kuchinawa, in the place of it.
In Nadeko’s class, the atmosphere has become strained and because Nadeko is the class rep, she’s been pressured to do something about it. Later on, Kuchinawa tells her to go to the shrine where she last sacrificed snakes in Bakemonogatari. He commands her to atone for what she did by finding the remains of the snake god that inhabited the shrine in the past.
She tries not to involve Koyomi, but he manages to find her at night and takes her to his house. She wakes up next to Tsukihi and manages to bring up the topic of Koyomi’s girlfriend. Finally, Nadeko reveals her jealousy toward Hitagi, but claims that she would never try to steal him. Tsukihi says that she planned to support her if Nadeko was going to do so. However, since Nadeko instead said she doesn’t want to trouble him, Tsukihi says it’s as if after all these years passed, that Nadeko is using her brother as in excuse to reject boys from her school. Tsukihi loses her patience and suddenly cuts Nadeko’s fringe. This way, she wouldn’t be able to hide her face or emotions anymore, which she later attempts again with her teacher. Yet without her fringe, he can see that she isn’t disturbed at all. Nadeko ended up very “uncharistically” snapping at him and after, to her classmates. The serpent then tells Nadeko that its remains are in Araragi’s house, where she finds the paper charm Gaen previously trusted Koyomi with.
Kuchinawa offers to grant Nadeko any wish, and she already knows what to ask for: Koyomi to love her back. She says this in front of him, but he says that her desire cannot be granted. After some of Shinobu’s provocation, Nadeko eats the charm and becomes an oddity, sharing her body with Kuchinawa, and her hair turns white with each lock becoming a snake.
As an oddity, Nadeko reveals her true colors: an obsessive, egotistical, cynical girl, who would not hesitate to kill in order to keep her delusional and impossible love story.