Tsubasa, the main character of Tsubasa Cat, is Koyomi's classmate and the class representative. Koyomi describes her as "the class representative of all class representatives." Prior to the novel's beginning, she was possessed by a bakeneko during Golden Week due to stress over her family. Although it has since been resolved with the help of Shinobu and at the cost of her own memories, the problems emerge again right before the school festival because of different stress. It was revealed by the bakeneko at the end of episode 14 of the anime that the source of the aforementioned stress was her feelings for Araragi. The stress was so severe that the cat resurfaced again after only 2 weeks of Hitagi and Koyomi started dating, compared to the 17 years of stress that Tsubasa got from her family. Despite Black Hanekawa possessing a female body, the spirit itself is male. When Tsubasa turns into Black Hanekawa, her hair turns into white and she grows cat ears.
Tsubasa Family tells the story of what happened during the nightmarish Golden Week when Tsubasa was possessed by a cat. On the first day of Golden Week, Koyomi, after thinking that he was in love with Tsubasa, went out and stumbled upon Tsubasa with a bruise on her face caused by her "father". Shortly after, Tsubasa and Koyomi found a dead white cat without a tail beside the road. Tsubasa, then picked up the cat and asked Koyomi for help in burying it. Throughout the whole week, a monster cat has been rumored to be seen attacking people. Oshino said that the oddity itself is a weak spirit, but having possessed Tsubasa gave it knowledge and strategy strong enough to rival even a vampire. If Black Hanekawa doesn't disappear soon, Tsubasa and the cat will merge with each other and the only way to stop Tsubasa is by killing her. It is interesting to note that Black Hanekawa has the verbal tic of changing words with "na" to "nya". In the anime, despite the flashback in Tsubasa Cat being severely different from the novel, it is not retconned.
In Tsubasa Tiger, while on her way to school, she met a gigantic tiger named Kako that has the ability to talk. It was revealed that the tiger was created by Tsubasa because of feeling envy that her "parents" are getting closer to each other, similarly to how Tsubasa used stress to make the second appearance of Black Hanekawa. If she had never resolved her problems, she would continue to create cat-like animal oddity based on her negative emotions, getting stronger each time. Revealing that Tsubasa does not feel pity and treated everyone as an equal, that was one of the reason why the sawarineko tried to help Tsubasa relied stress. Tsubasa Tiger was written in Tsubasa's perspective instead of Koyomi's. Her catchphrase is "I don’t know everything, I just know what I know." Koyomi stated that he respects Tsubasa more than anyone else.
What's scary to note about Tsubasa is that all kai specialist noted her as "dangerous". Meme was wary of the first time he met Tsubasa, Episode thought that something was off about her and Kaiki stated that the person who arranged the meeting between him and Karen during the events of "Karen Bee" was not normal. Kaiki later on stated that he had no idea about Tsubasa nor any information on what she is like, but that he will try to runaway just to never meet her if the time comes. Tsubasa is so unnatural that in the near future, she would essentially become the second coming of Gaen. That is partly the reason why Black Hanekawa became a monster-class oddity despite the sawarineko being a low-class oddity because it had possessed Tsubasa. If the sawarineko possessed somebody else, it would not be as strong as when it possessed Tsubasa.
