Su Won

When Yona was born, Soo-Won approached her to greet her, but King Il did not allow him to come closer and scared him away, expressing hostility. Another time, when Soo-Won and Yona were playing and were about to enter the Hiryuu Mausoleum together, King Il said that the mausoleum was not the place for him. On the night that Soo-Won avenged his father, King Il told him that he would never become the Red Dragon King and that Yona, the rightful heir, would lead him to his death. Soo-Won is skilled in swordsmanship and other weapons thanks to his sword master and later bodyguard Hyu-Ri. Son Mundeok trained him in archery and spearmanship at an early age, much like Haku. This is confirmed in the anime when he demonstrates amazing abilities in a mock fight against Gun-Tae, a general of the Earth Clan known to be one of the most powerful generals. Soo-Won also demonstrates great political competence in dealing with the Five Generals, as well as mastery of strategy, as shown in the mock battle. Politics is his favorite field, and he demonstrates amazing people skills; however, this does not mean that he is not a great warrior himself. Although he was shown to not be as strong as Haku early in the series, he has shown to be at least close to his strength. Soo-Won is a highly intelligent, cunning, and resourceful individual; these traits have made him one of the best strategists, if not the best, shown in the series so far. One example of his abilities is his horses' tiger-like attire, which he used to scare his enemies. This tactic gave his men enough time to attack before the enemy could react. His intelligence and charisma, as well as his martial prowess, were enough to gain the support of four of the five Clans (the Wind Clan being the only exception due to their loyalty to Haku) and solidify his power as the ruler of the kingdom.

Soo-Won admired his father so much that he was willing to overlook many of the atrocities Yu-Hon committed during his life, such as the controversial Shin incident. After his father's death, Soo-Won was devastated. He gradually became an increasingly secretive person, plotting his revenge. For this, he was willing to break away from Haku and Yona and ruin his relationship with them just to achieve his ambitions. Despite his heartlessness, he still genuinely cares for his childhood friends, which was evident when he learned of Yona's death or how he was unable to draw his sword after seeing the anger and pain with which Haku lashed out at him. Soo-Won was born in Hiryuu Castle to General Yu-Hon and Lady Yeon-Hee, and lived there for about 8 years of his life. After his mother had to move to a separate residence for treatment, he joined his father and visited Hiryuu Castle during Clan gatherings, as well as often spending time playing with his close childhood friends, Yona and Haku. His relationships with his friends made him happy, and he dreamed of them remaining friends forever. However, this dream became impossible to fulfill when he was forced to choose between his friends and revenge and usurping the throne. When Soo-Won was 9 years old, his father was assassinated by Emperor Il while they were on a long horseback ride together, although the murder was passed off as an accident. Since then, Soo-Won harbored a secret hatred for the emperor and quietly plotted his revenge so that he could become king himself and fulfill his father's dying wish to restore Kouka as a world superpower. Knowing that this plan would ultimately separate him, Yona, and Haku, he kept silent about his plans and continued to live as if nothing had changed. At some point, Emperor Il revealed to him that Yona is the reincarnation of King Hiryuu and is different from him. It is later revealed that King Il has always been hostile to Su-Won, even when he was a small child.

Not only did he remain oblivious to Yona's feelings for him, but he also began to doubt them a decade later. As a child, he attended numerous marriage negotiations with various women, but showed little interest in relationships. This trait was so notorious in the castle that it even led many to speculate that their king might have a different sexual orientation. As a king, he does not think much about finding a spouse, and as Lili noted, the only thing he sees in it is political gain. However, he has a surprising understanding of how interactions between adult men and women work, as shown when he tells Yona that he can no longer sleep with her like he did as a child. Due to his frail frame and poor combat skills, some consider him weak, and often pit him against his childhood friend Haku, a martial arts prodigy. In fact, he never shows his true strength unless it is necessary. When he does show it, he is considered a skilled swordsman, even capable of threatening General Lee Gun-Tae. Above all, he is an excellent tactician and a formidable strategist. He can devise a battle strategy that will effectively lead his troops and effortlessly manipulate his enemies. Soo-Won is very goal-oriented and ambitious, to the point that he will even defy the will of Heaven if necessary. Just as his father, Yu-Hong, disliked anything related to the divine, Soo-Won rejects the will of the divine and emphasizes throughout the series that he only cares about the "strength of the people". He has a deep love and pride for Kouka and makes it his goal to restore its greatness and protect it from foreign invaders, especially the formidable Kai Empire. Soo-Won also admires strong people. He idolizes his father, Yu-Hong, who was a strong but bloodthirsty warrior, and aspires to become as strong as him.

He feigns naivety and carefreeness if it serves his purposes. This is not only a genuine part of his personality, but also a tactic he uses to make his enemies underestimate him and distract them. He trusts no one, believing that no one in the world is selfless, including himself. From a young age, he was extremely outgoing and curious, often going out of his way to gain new experiences and learn new things. He is also not the type to try to live on his own. Once he gets involved in something, he is very proactive, and usually has a strong belief that he will achieve his goals together with the people around him. However, despite all his sociability, he tends to be secretive about sensitive issues such as his personal life and past. According to Ohgi, Soo-Won was a person who was interested in everything, but never talked about himself. He also has a habit of changing the topic of conversation or evading it if someone catches him in a lie or doubts his intentions. He is a man of few words, not very expressive, and sensitive. Lily noted that he can sometimes be caught frozen in thought and introspection. In their youth, Haku noted that Soo-Won is interested in all people and all things equally. Soo-Won has an approach to everyone and never judges anyone for their appearance or social status. Because of this, at a young age, he forms connections with different people, even those who seem rude and unsociable. Due to his broad outlook, Haku understands that Soo-Won has the potential to become a great king, and admires him to the point of wanting to become his right hand. Despite his extraordinary charisma and friendliness, Soo-Won understands nothing about romantic love. Yona once remarked that Soo-Won is like a child in such matters. In a conversation with Lily, he himself notes that he has little understanding of how it works.

Soo-Won-Eom is 18 years old and 185 cm tall. His birthday is February 3. He has light brown hair and green eyes. Su-Won is the current ruler of the Kouka Kingdom, the 11th king of the Sky Clan, and the tritagonist of the manga and anime. He is the son of General Yu-Hon and Lady Yeon-Hee, the older cousin of Princess Yona, and a childhood friend of Haku. He killed his uncle, Emperor Il, to avenge his father's supposed murder. He currently resolves Kouka's internal conflicts to restore the country to its former glory, like the reign of his grandfather, Emperor Ju-Nam. Soo-Won is a tall young man with soft, gentle features, similar to his mother, Yeon-Hee, and his father, Yoo-Hong, in height. He has sea-green-blue eyes and white skin. His dark blond hair, which falls just above his shoulders, is usually tied in a ponytail with a gold decoration (in the manga, it was a small ribbon). As a child, Soo-Won wore his hair loose and shoulder-length. Yona thought of him as "cute as a girl", but as he grew older, his features became more masculine, while still retaining some of his softness. Soo-Won's subjects find him attractive. In the anime, Soo-Won wears a simple white robe with a purple sash and a purple hem. Throughout the manga, Soo-Won wears upper-class clothing typical of nobility, including a yellow cape worn by kings. Soo-Won is a complex character. Most of the time, he acts calm and cheerful. He has a great deal of emotional strength and maturity, and was even able to remain calm when his father died at the age of 9, unlike the other adults in the room. He can adapt to any situation. He acts friendly towards those he likes, but underneath his smiling facade, Soo-Won is a very calculating person. He has keen observation skills that help him see people's true intentions.