Inheriting a mummified hand from her mother, Suruga first wished on it in 4th grade to run quickly so that she could win a local race. Soon after, four of the competitors were hospitalized due to an assault from a monster dressed in a raincoat. Suruga suspected the hand may be acting like a monkey's paw, wherein a wish is granted in an unexpected way. She abstained from wishing upon the arm for many years, coming close once to wish for help with Hitagi's crab problem, but it's stated that such a wish would probably not have been granted, as the arm only manifested negative wishes, especially the hidden intentions of them (the students being beat up was revenge for Suruga being outcast). However, after seeing Koyomi and Hitagi in a relationship, she became insanely jealous, and wished upon the arm to be with Hitagi, without noticing that the hand had grown into an arm and attached itself to her. Oshino surmises that her first granted wish had already caused the devil to take a portion of her soul, leading to the hand's growth. He offers the solution of cutting off the arm, a suitable price in exchange for nearly killing Koyomi (a result of the hidden side of her second wish). Koyomi objects to this, and instead, opts to defeat the devil to dissolve its contract. To prepare for the fight, he gives some of his blood to Shinobu in order to boost his limited vampiric powers. Despite that, he still gets literally shredded apart by the devil, and is saved at the last moment by Oshino's intervention. He called for Hitagi, who notes that Koyomi had hidden the entire situation from her, against his precondition for their relationship. With her appearance, the devil is unable to continue the attack without invalidating either half of the wish, so the contract is dissolved. However, even though the devil is gone, her arm still hasn't fully recovered. In the end, she becomes good friends with both Koyomi and Hitagi.
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