Koubun Ka is a tall man with black wavy hair tied back and yellow eyes. He has markings on his face. He wears a tall hat, with traditional and wealthy looking clothes. He carries around his Household Vessel, which takes the appearance of a green fan.
He is a cold and calm person, but seems to be more cheerful when he isn't working as Kougyoku's assistant. However, he has admitted to trying to manipulate her and his subordinates into doing what he wants, though it seems that he is not very good at this.
Koubun was born in a poor village in the North Province of the Kou Empire. He passed the National Exam with high results and was assigned as a Government Official.
When he was 17, he became Kougyoku Ren's assistant and helped her gain confidence. From that moment on they have always been together.
Koubun Ka arrives in Balbadd, at the Fog Troupe's base, along with Princess Kougyoku. They save Judar after his defeat to Ugo. Koubun notes that they barely managed to save him. Upon hearing it, Kougyoku adds that he's badly injured and commands him to save Judar, as it won't be a joke if he dies. Koubun answers that he understands, calling Judar their precious "Oracle". When Kougyoku decides to fight Ugo, he tells her to be careful. After killing Ugo, Kougyoku comes back to Koubun and asks him how she did. Koubun only answers "As expected from the Princess". When asked about Judar's condition, he explains that even though he's giving him an emergency treatment, they'll need a standard facilities for a full recovery.
As they are about to leave, Aladdin attacks them. When he explains that Ugo was on his and his comrades' side, Koubun asks Kougyoku what is she going to do. After Kougyoku is stopped by Sinbad, she orders everyone to leave, much to Koubun's surprise. He stays next to his embarrassed Princess during their way back.
Some time after, Koubun is with Kougyoku at Balbadd's Palace. Kougyoku asks him about Judar's injuries. He says that although he used his Household Vessel, his bones are all shattered and it will take some time until Judar is fully recovered. Kougyoku answers only "Is that so...", so Koubun asks her if she's alright. She asks him if he doesn't find it weird why a conventional princess such as herself has been selected for this political marriage, instead of Hakuei Ren, since she is the daughter of the former Emperor. Koubun explains that Balbadd is a strategic location needed by the Kou Empire and to obtain it perfectly as well as the citizen's trust, they need a conventional princess such as Kougyoku to become a queen. Kougyoku tells him that she went through a lot just to conquer a Dungeon and she has longed to progress down the path of a warrior. She also wanted to try falling in love for once. Koubun seems worried about her, but explains that this is the Emperor's order and her brother will attend the ceremony as well.
Afterwards, Koubun accompanies Kougyoku when she hears the commotion done between Alibaba Saluja and his brothers. He listens to the conversation between gathered and is shocked when Alibaba announces that there won't be a new king after Ahbmad Saluja's dethroning.
Koubun also stands silent when Kougyoku shares her views on Balbadd's situation and all of its rights in Kou's hands. When Alibaba says that they were made by the previous king and the country of interest has been destroyed, Koubun realizes that it's meaningless quibble. He understands that the two matters are not related and there isn't a reason why they would be formally cancelled. When Kougyoku answers "Meaningless...", Koubun nods his head and thinks that it would be good to return the argument now. However, he is quite shocked when Kougyoku starts her asking what will happen "if she return". He also doesn't want Kougyoku to go along with Alibaba's reasoning and is happy when she exclaims that she won't do it.When Sinbad steps in in the negotiations and Alibaba mentions Sindria and Balbadd having good relations, Kougyoku asks Koubun if it's true. He confirms it, but adds that this two matters are unrelated. He is sweating in shock when Kougyoku eventually agrees to leave this case to His Majesty would be the best. When Kougyoku leaves the room after all of this, Koubun follows right after her.
After that, Koubun returns with the Princess and other subordinates on a flying carpet to the Kou Empire. Koubun asks if it's fine to leave Judar there, but Kougyoku exclaims that it is, as she left him in Banker's hands. Seeing Kougyoku happily talking about Sinbad, he sighs. Then, on of his subordinates points out that the group of people is gathering. Kougyoku, still brightly smiling, says that she knows about it and asks if it isn't outside the Palace, but the man notes that they are heading straight towards the Royal Palace.
Koubun arrives in Sindria together with Kougyoku and her cousin, Hakuryuu Ren. Sinbad greets them respectfully but is suddenly attacked by Kougyoku who accuses him of defiling her body. Asked what is the meaning of this, Kougyoku starts crying, so Koubun interrupts. He explains that it's too harsh for her to tell the whole story from her mount. He notes that it's the testimony from the Princess herself and, points out at the soldiers, saying that there are also other witnesses. He begs them to take it as the truth. Then, he begins to recreate what has happened according to Kougyoku herself.
Koubun explains that when Kougyoku woke up in the morning, when she looker around, she noticed a sleeping, naked Sinbad in her bed. Kougyoku cries and promises to kill first him, and then herself. Sinbad says his version of events, so Kougyoku tells her own. Asked by Ja'far what does she mean, Koubun, in her place, answers that King Sinbad noticed Kougyoku during the banquet, he made her faint and after this, the act occurred. Koubun suggests that in this case, in order to take responsibility, Sinbad has no other choice but to marry Kougyoku. Her honor would not take any damage and even her father, Koutoku Ren, would have no problem with giving his daughter to a High King of Seven Seas. Upon hearing that, Sinbad orders Yamraiha to prove his innocence with Magic. Kougyoku steps out to her, so Koubun, shocked, tries to stop her, but she replies that she wants to know what really happened.
Yamraiha is able to dispel doubts of Sinbad actions by using her magic, Sharrar Raqesa, to re-create the true events of the night in question. Kougyoku believes that what she saw is true, so Koubun tries to persuade her that she's being deceived. He accuses Yamraiha of orchestrating something in order to protect Sinbad and points out at him, saying to accept his sins. Kougyoku stops him, admitting that she also thought something was out of place but she panicked. Kougyoku apologizes to Sinbad for causing the commotion and starts crying, with Koubun and her subordinates by her side.
Looking at his sad Princess, Koubun, in his thoughts, introduces himself and begins to remember his past, the difficulties he went through and what happened after meeting Kougyoku. He then says that his dear Princess went through such a difficult experience because of someone but admits that he's the culprit himself. He recalls what happened that night: he made his two subordinates to escort Kougyoku and then, used the chance and made her faint. He brought her to Sinbad's room and hoped for Sinbad to be accused of disgracing Kougyoku. He admits that he had a scheme in the past, that after Kougyoku married the King of Balbadd and gave birth to heir, he would become this child's guardian, which was the plan to seizing the power in this state. The plan failed so he came back to Kou and thought what to do, when Sinbad payed them a visit. He realized that he was perfect for this, since he would b able to seize the power and the Princess would marry the person she loves. He says that his primary ability is to read the hearts of people and then using that. He calls it "Heart Manipulation Technique". Thanks to that, he was able to make many allies, including the subordinates that helped him with his scheme.
Koubun decides to stay strong and push his decision through. However, his faithful subordinates, seeing how sad their Princess is, confess that it's all Koubun's fault. Shocked, he asks them what about their promotion, but they answer that they're her subordinates, not his. Then Sindria's soldiers start attacking him as the traitors that wanted to frame King Sinbad. He tries to protect himself but gets hit by Hakuryuu. The Prince, exasperated with his countrymen's behavior, formally apologizes to Sinbad on their behalf. He forces to Koubun to admit that he's also sure that Yamraiha's magic showed truth. The subordinates comment that Koubun made him fall on his knees for such a reason, but Koubun orders them to be quiet. He falls at the ground and starts crying. He laments that vulgar and dirty trash like him can't have any dreams, but Kougyoku reassures him that he's splendid person. While crying in Kougyoku's arms, he thinks that if he apologizes with all his strength, they will forgive him. Just then, Ja'far passes them by and spittles at him.
When Judar comes to infiltrate Sindria, Koubun assists Kougyoku when she goes to see him. He realizes that they've been surrounded by Sindria's citizens and looks annoyed about this fact. He has the same expression when Judar leaves after the talk with the Princess.
During the Dungeon Conqueror's Banquet, he looks somewhat depressed. He then explains the arrival of Judar to Hakuryuu. He explains that now, they've become the most unwanted guest in Sindria and asks if they should leave this country immediately. When drunk Kougyoku starts saying that she doesn't want to return yet, Koubun reacts quickly, reminding her that he told her to not have alcohol. He worries about her when she tells him that her father and others would be fine without her. He looks shocked seeing her talking about how Sinbad let her stay here forever. Afterwards, he asks Hakuryuu about his intentions and learns that the Prince also wishes to remain in Sindria for a little while. When Hakuryuu's arm starts throbbing and he cries in pain, Koubun asks him what's wrong.
After some time, he asks Kougyoku to get hold of herself while trying to wake her up. Just then, smiling Ja'far arrives. Terrified Koubun recalls what Ja'far has done to him earlier. Ja'far proposes him to have some alcohol and even though he denies the offer, Ja'far still takes him nonetheless. When Hakuryuu loses his arm, Koubun comes to aid him.
Later, Koubun interrupts Kougyoku's time in the garden. He tells her they've received numerous orders to return to the Kou Empire immediately. She terrifies him by saying that she doesn't want to go home yet, but she quickly laughs it off, telling him to not fall for it. Afterwards, Koubun is looking for Kougyoku when she disappears to see Alibaba. He watches the fight between Kougyoku and Sinbad amazed but shocked when Kougyoku releases her Extreme Magic, Vainel Ganezza. He falls asleep due to Sinbad's Djinn's, Zepar's Sound Magic. He wakes up a little before Kougyoku.
When Kouen Ren arrives at the palace, Koubun reminds Kougyoku that she has to talk to him. Later, he follows her on her way to Kouen's room, but as they reach their goal, Kougyoku dismisses him and other attendants. The next day, he follows Kougyoku at the Emperor's funeral.
When Kougyoku receives an order from Kouen to join him immediately and responds, Koubun is behind her, bowing deeply.
Koubun accompanies Kougyoku when she comes to see Alibaba in the Balbadd Palace.
- Koubun Ka's Household Vessel: Koubun Ka has an unnamed Household Vessel that uses the water of Vinea for healing.
Koubun cares deeply for Kougyoku and is always protecting her. He's also her mentor in fencing, but tends to hold back, much to her annoyance.
- His first name means Yellow Writings. His last name means Summer.
- "Koubun" is the Japanese pronunciation; in Chinese his name would be Huángwén.
- Koubun would like to be promoted.
- His weakness is Kougyoku's wilfulness.
- His (self-proclaimed) special skill is understanding the human nature.
- In Volume 27's omake when asked who he wishes were his real sibling, Koubun chose Kouen Ren as his little brother and saying: "In other words, if I become the first prince... this country will be mine!" Kouen comments: "Channel this ambition into protecting Kougyoku. Still, I won't promote you."