Nekomonogatari Black: Tsubasa Family

It's the beginning of Golden Week, before the events of Bakemonogatari. After Tsukihi kicks Koyomi out of bed, he takes the opportunity to ask her about his growing feelings for a new classmate of his, wondering if he has fallen in love with her. Tsukihi deduces he is merely sexually frustrated and suggests he buy some porn magazines to relieve himself. After a brief meeting with Karen, Koyomi leaves home on his bike, on the way encountering Tsubasa Hanekawa, his classmate, sporting a large bandage on her left cheek. Tsubasa confesses to him that she was hit in the face by her foster father and asks Koyomi to not tell anyone about it, offering to grant any request in exchange for his silence; however, Koyomi only asks her to let him use his blood to heal her wound.

Koyomi pays a visit to Oshino bringing him some donuts, but ends up giving them to Shinobu instead. Oshino asks Koyomi about his encounter with Tsubasa and learns from him that after having her wound healed, the two of them came across a dead silver cat with no tail, which Tsubasa buried. Oshino realizes that they had encountered a Cursed Cat (障り猫 Sawari Neko?) and asks Koyomi to look for Tsubasa while he investigates the buried cat. Later that night, Koyomi comes across Tsubasa, possessed by the cat and dragging her unconscious parents along with her. Koyomi tries to stop her, but she flees after tearing off his left arm. After calling an ambulance for her parents and reattaching his arm, Koyomi wakes up at Oshino's place beside Shinobu and learns from him that he had been asleep for over twelve hours, and that Shinobu has been staying beside him to help his recovery. Oshino also claims that Tsubasa is now beyond help and leaves to confront her after asking Koyomi to stay out of his way.

Koyomi breaks into Tsubasa's house and is shocked to discover that she does not have her own room there. He rushes back home, where he learns from Tsukihi that people all over the city are being attacked by a mysterious cat-girl (化け猫 bakeneko?), who her realizes must be Tsubasa. When classes resume and Tsubasa never comes to school, Koyomi seeks out Oshino, who informs him that after challenging the Cursed Cat twenty times he was unable to defeat it even once. Although a Cursed Cat is usually a weak type of Oddity, this one has made use of Tsubasa's outstanding intelligence to outsmart him. He also warns that the cat must be stopped before its conscience merges fully with hers or rescuing Tsubasa will be impossible. The following day, Koyomi meets the cat, who asks him to stay out of its way, claiming that it will eventually return Tsubasa's body to her once it manages to relieve her of all her stress. Unable to stop her from leaving, Koyomi realizes that his feelings for Tsubasa have surpassed even love, proclaiming that he is ready to die for her if necessary.

After Koyomi spends several days begging for Shinobu's help, she entrusts him with the demon sword (妖刀 yōtō?) "Heartspan" (心渡 Kokoro Watari?), able to kill Oddities without harming the humans they possess. Koyomi manages to lure Tsubasa to Oshino's place by sending her an e-mail claiming he is under attack by a vampire, but instead of comforting her, he berates Tsubasa for allowing herself to be possessed, prompting her to attack him. After Tsubasa slices Koyomi's body in half, it is revealed that it was all part of his plan to have herself cut with the sword, which was concealed in his body. However, Tsubasa refuses to let the Cursed Cat leave her body, and Shinobu appears to restore Koyomi's body and bring Tsubasa back to normal. The next day, Tsubasa has returned to her normal life with no memories of what happened. Oshino suggests Koyomi marry Tsubasa in order to give her the family she always wanted, but he replies that despite truly caring for her, he would never be able to fall in love with her. Some time later, Koyomi is about to meet Hitagi for the first time, leading to the events of Bakemonogatari.