Gotsutotsukotsu

In the anime, she is a warrior who appears and tries to make several failed assassination attempts on Gien. She later confronts Gien with a group of her allies and tries to kill her yet again, but fails yet again due to Batai coming to Gien’s aid. The reason she tried unsuccessfully to kill Gien was that during a martial arts competition, Gien accidentally killed her older sister in the heat of battle. Kotsu thinks that Gien had to have cheated to have won, as her sister was very strong. Batai convinces Kotsu that Gien herself is strong and has honor, thus won the fight fairly. Kotsu concedes this, but Gien still killed her sister, so she claims that she’ll become stronger herself and come back to kill Gien someday. She is last seen running back into a forest.

*In history, Gotsutotsukotsu/Wu Tu Gu/兀突骨 was one of the Four Heavenly Kings of the South.