This article contains details from the manga that are not covered in the anime. Proceed with caution.
Hiyou has light colored hair, tired light colored eyes and a scar almost parallel, on his forehead. He wears traditional clothing, which has lots of little floral-like details. He is said to be around 35, but appears much more youthful than his true age.
Hiyou seems to lack empathy.
He does not seem to have any compassion for others and shows little emotion besides hatred, contempt and anger. He also expects compensation if he has helped anyone before and has little patience for anyone unable to do so.
He is bitter and harsh, often using force and violence if he does not get his way. He views other people as disposable, as Tetora points out that when he stabbed her, he could have stabbed his own guard. Hiyou replies that he would have just found a replacement "drug puppet", as he puts it. He is also shown to be vain and self-obsessed, as he is often shown fretting over his appearance in a hand mirror. When he receives another scar on his face from Yona, he viciously orders for her to be assassinated, becomes erratic and psychologically unstable in his need for revenge.
He has no mentioned background.
Hiyou is first introduced by a courtesan named Arin, who works in one of the many brothels and businesses he owns. She explains to Kija, Hak and Jaeha that he owns many places in Shisen which all sell nadai and nadai-laced drinks. He is revealed to currently be at the very inn that Yona, Lili, Ayura and Tetora are staying in.
As Tetora is retrieving some tea for the rest of the girls, she happens to overhear a conflict between Hiyou and inn's owner in a room nearby to theirs. The inn's owner was refusing to sell nadai in his inn, prompting Hiyou to point out that he'd helped keep the inn afloat financially. Just as Tetora overhears this, she is confronted by one of Hiyou's bodyguards, who she attacks. She is shocked to find her fighting technique doesn't effectively incapacitate the guard, as he is drugged and thus his sense of pain dulled. Just as she realizes it, however, Hiyou himself stabs her through the door of the room.
The commotion leads Lili and Yona to come looking for Tetora, finding her crumpled on the floor and bleeding. Yona, still holding her sword from an earlier practice session, decides to step in and defend Lili and Tetora. Though she sustains a slash to her back, she is able to hold off Hiyou's guards for long enough that Zeno, Yun and Shin-ah can come help fight off the guards. Shin-ah fights off the remaining guards, but stops at Hiyou, as Yona wants to interrogate him. As Yona approaches, Hiyou makes an attempt to pull out his sword. Yona beats him to it, slashing his forehead in a warning not to move. Given his vanity, he is rendered psychotic by this new mark on his face, and he manages to escape the inn but not before swearing revenge on Yona.
True to his word, Hiyou soon sends assassins after Yona. However, since Hiyou's men are all on nadai, they begin targeting any random woman they come across regardless of if they look like Yona or not. One of these women is Lili, who is unwittingly rescued by Suwon and ends with the two of them deciding to team up to stop nadai trade. As his men fail over and over again to capture Yona, Hiyou grows more and more unstable and his obsession with revenge more all-consuming. He sends to Southern Kai for his allies in nobility, who come by boat, bringing soldiers. The fleet is quickly sunk by Hak's group and some of the Water Tribe army, while Yona's half of the group (along with Suwon and Lili's men) pick off the rest of Hiyou's men.
Seeing his plans crumble, Hiyou leaves his place of hiding to find Yona personally. Once found, he attempts to charge at her with a dagger, but instead stabs Hak in the arm last minute. He is defeated and presumably arrested after Hak delivers a devastating punch to his face.
Although Hiyou mostly relies on multiple bodyguards to protect him, he is capable of wielding a sword with enough strength to stab Tetora through a door. Additionally, he has many powerful connections in other nations.
- (To an unnamed innkeeper) - "You're really useless to me."
- His line about threatening to "cut the meat from (Yona's) breasts and crotch" was originally only supposed to stop at breasts and the second part was added by some sort of editing mishap. However, Kusanagi decided to keep the mistake, as she felt it accurately represented Hiyou's disturbing mindset.