Karen Araragi (阿良々木 火憐, Araragi Karen) is the eldest of Koyomi's sisters and the older half of the Tsuganoki 2nd Middle School Fire Sisters (栂の木二中のファイヤーシスターズ, Tsuganoki Ni-chuu no Faiya Shisutazu). She is a self-proclaimed "hero of justice" who often imitates the personality and quirks of various characters from tokusatsu series. Despite this, she is completely uninvolved with the supernatural, until she becomes victim to a certain oddity.

Personality:
Befitting her name, Karen is a hot-blooded girl who acts as if she is a superhero who has the duty of protecting others from danger. She likes to imitate characters from various tokusatsu live action series like Dekaranger; fortunately, she manages to pull it off due to her flexibility and quick reflexes, which was a product of her constant exercise and training, which involves practicing karate and capoeira, among other martial arts.

Her personality often collides with Koyomi's more laid back personality more recently, especially since Koyomi has developed a certain degree of anxiety over his sisters' safety due to his experiences with the supernatural. In fact, he has called Karen's habit of acting like a superhero alongside Tsukihi a "travesty".

Tsukihi mentions in later episodes of Nisemonogatari that Karen has a boyfriend named Mizudori, but that they haven't been getting along very well.

Background:
Karen, during the time before Koyomi's transformation into a vampire, often had sparring sessions on judo with her older brother. She eventually notices that Koyomi stopped attending judo sessions with her.