She is both Koyomi's and Karen's younger sister. She is the supposed younger sister of both Koyomi Araragi and Karen Araragi, and the youngest member of the Araragi family. She is the younger half of the Tsuganoki Second Junior High School's Fire Sisters. She is unknowingly an offspring of the Shide no Tori, making her a fake human and giving her traits similar to that of a phoenix. She is nicknamed Rara by her childhood friend Nadeko Sengoku. Unlike her sister Karen, she prefers doing indoor activities. Contrary to her personality, she is emotionally unstable to the point that Koyomi describes her as having hysteria. Rosokuzawa is mentioned to be Tsukihi's boyfriend by her brother, and she says she's in love with him but has a chaste relationship. Despite being a member of the Fire Sisters, Tsukihi admits that she doesn't have the drive to do things like her older sister, although she says that she shares her siblings' belief in justice. She's also a bit airheaded at times. Also like her sister, she doesn't believe in oddities or the supernatural, despite being one herself. She is 13 years old.
