Bakemonogatari: Hitagi Senjougahara

Hitagi, the main female character of Bakemonogatari, is a weak-looking girl with an "incurable disease." She is in the same class as Koyomi, but he has almost never heard her speak. When she was in the first year of high school, she encountered a mysterious crab, after which she became nearly weightless. Ever since then, she has avoided contact with everyone else, threatening everyone who discovers her secret. She called herself a tsundere and always speaks in an abusive style.