Setsuna Imawano (忌野刹那) is Shizuru's older sister who used to be very close with her. She was a genius of the Juugondō, which made her father, the head of the Juugondō, feel threatened. He tried to have her assassinated and used Shizuru as a hostage, and so she disappeared, leaving Shizuru distraught but safe. She turns up when her father comes to Tokyo, and kills him immediately with the other members in a coup, leaving her in control of the Juugondō. She later attacks the Agency and kills most of the agents, except for Kagura, Kensuke, Kyouko and Iwahata.
Setsuna is a skilled fighter, able to easily toy with Kensuke. She has the "Eye of Satori," a telepathic ability that enables her to read minds. As a consequence, one of her eyes is remarkably different from the other. She has a spirit beast, a water-using ogre-like creature called Suiko (Water Tiger). She is ruthless and ambitious, willing to kill her own sister and subordinates. Her goal was to set the world into eternal war.
During the fight in Tamamo's garden she killed Kensuke; however, after using the power of the Kyuubi, Kagura revived him. During the cataclysmic event when the Kyuubi was came into being again, Setsuna lost an arm to protect Shizuru. She has disappeared from the hospital, and since then Shizuru and Izuna have been tracking her down.