Monogatari Series: Second Season EP12 - Nadeko Medusa, Part One

Fully transformed into an apparition, Nadeko confronts Shinobu and a battered Koyomi who attack with the intention of killing her, and envious of their relationship, she stabs Koyomi's heart. The story then retrocedes to some days before, in Halloween, when Nadeko, on her way to school has a short encounter with Ougi Oshino, Meme Oshino's niece, who is also a first year student Koyomi's high school. For some reason, Ougi claims that it is about time for Nadeko to stop always playing the victim before she leaves. At her school, Nadeko starts having visions of white snakes and calls Koyomi for advice, and they agree to meet at 10 PM at his house, as by that time Shinobu must be awake to provide some help. Soon after, Nadeko hears the voice of a snake instructing her to meet it at the shrine where she used to kill snakes instead and there it reveals itself as the giant apparition snake, Kuchinawa, who demands compensation for its fellow white snakes she killed by asking for a favor, to which she agrees.