Tsukihi, the main character of Tsukihi Phoenix, is one of Koyomi's sisters. She's the youngest of the Araragi family. Unlike her sister Karen, she prefers doing indoor activities. Contrary to her personality, she constantly changes her hair style and is short-tempered to the point that Koyomi describes her as having hysteria. She is actually the reincarnation of a phoenix and has been since before she was even born. The phoenix entered the baby's body when it was still in the womb and by now both beings' minds have become one. She is immortal, except the only thing that can end her life is a natural death from old age.