Kokuton has a bull-like appearance; lion-like hair, a tail and his entire body is covered in fur. He has a horn on each side of his head. He wears Kou's traditional clothing and has a shoulder protector on his right shoulder. He has Kou's emblem in the chest of his armor.
Kokuton attends at the Emperor's funeral and is located with the rest of the court, with the traditional mourning attire.
When a priest reads the testament and Gyokuen Ren is appointed the next Emperor, he, Shou En, Kin Gaku and Seishuu Ri rise up, enraged, because Kouen was supposed to be the next Emperor. Kokuton and the others listen at Gyokuen's explanation of her being the next Emperor instead of Kouen, but they know they have been fooled. Immediately after that, the court splits in two, with Gyokuen and the Imperial Priests in a side, and the army and the Imperial Family in the other.
Alibaba Saluja is fighting against the Black Djinn, and is about to use his Extreme Magic to eliminate them when Shou En advances to his move and destroys them with a breath of fire. After that, Kouen and the other monsters make their appearance riding carpets. Kouen analyzes the situation and, when he sees Kouha Ren's state, says to his Household that if the the enemies are too much for the others, they will deal with them with their strength. The four monsters roar in approval.
Kokuton, Seishuu Ri and Kin Gaku head towards the Black Djinn. Kokuton says that the Black Djinn have the same smell of the impure people who made a nest in their country. Then, they activate their Household and become huge monsters. His claws become longer and sharper, and begin to rip the Black Djinn.
After Alibaba has proclaimed that he stepped the batterfield in order to protect the third prince, Kouha, Kokuton says that the current situation isn't related to the truth in his words since there's no way to prove if he's telling the truth or not, but that there's a meaning in declaring that in front of everyone. He adds that if their young master would acknowledge him, then they will not be able to lay their hands on him anymore. Aladdin begs Kouen to send back his soldiers, saying that won't matter if they are from Kou or Reim, they will die. Kokuton, Kin and Shou En are surprised, and don't seem to understand what does he mean.
|“||Come, Household Born From Agares, I Consecrate My Body To You, Become One With Me!!||”|
- Assimilation: By saying this phrase, Kokuton takes on an even more monstrous and ferocious appearance. He becomes larger, and so does his claws. His claws become long and sharp enough for him to rip through a Black Djinn.
- Although he was introduced in Night 116, his name wasn't revealed until Night 182.
- His first name means Black Compassion. His last name means Circumference.
- "Kokuton" is the Japanese pronunciation; in Chinese his name would be Hēidūn.
- His design may be inspired by Minotaur of Greek mythology.
- He shares the same family name as Kokuhyou Shuu.