Yun is a 15-year-old male born on September 25, standing 162 cm tall. He originates from the impoverished Fire Tribe village of Touka, where he became an orphan at a young age. Forced to survive independently, he initially resorted to stealing. At age eight, he attacked the exiled High Priest Ik-Soo to steal rumored golden beads. Ik-Soo possessed no valuables but demonstrated kindness by trading his shoes for a potato to give Yun. This prompted Yun to abandon theft and begin crafting straw sandals for income. Though initially distrustful of religion and authority figures due to Ik-Soo's unjust exile by General Yu-Hon, Yun developed a deep bond with the priest. Concerned about Ik-Soo's inability to care for himself, Yun became his full-time caretaker, living with him in seclusion and suppressing his own dream of traveling the world to gain knowledge. Yun possesses a notably feminine appearance with bright blue eyes and short apricot-colored hair (blond in the manga), featuring long bangs parted to frame his cheeks and adorned with two small white feathers on the left side. His typical attire includes a light blue fringed cloak fastened at the neck over a pale green tunic tied with a yellow sash, brown wristbands over long sleeves, gray pants, and light brown fringed boots. He consistently carries a bag containing essential items like medicine and cooking ingredients. Self-proclaiming himself a "genius handsome boy," Yun takes pride in his intellect and appearance. His sharp tongue and tendency to insult others, particularly when the group acts rowdy or draws unwanted attention, mask a deeply caring nature. He prioritizes safety and survival, forged from his harsh childhood, but evolved beyond selfish instincts after meeting Ik-Soo. He now actively looks out for others, driven by a desire to emulate the priest's compassion – though he self-deprecatingly labels this as "self-satisfying hypocrisy." Possessing an eidetic memory for anything he reads, he meticulously records experiences and knowledge in a travel log. A significant aspect of his development is his growing determination to study medicine, spurred by witnessing suffering and death in Kouka and feeling inadequate to help. While harboring intense disdain for royalty and nobility, viewing them as "sly and filthy," this prejudice gradually softens as he observes Yona's transformation. He is easily moved to tears despite his outward sarcasm. Yun discovered the injured Princess Yona and her bodyguard Hak unconscious by a river after their escape from the palace coup and nursed them back to health. Initially resentful towards Yona due to her royal status and perceived ignorance of her father King Il's failings, he confronted her about her lack of gratitude and knowledge regarding the priests' exile. Influenced by Ik-Soo and witnessing Yona's resolve to change, he agreed to join her journey to find the Four Dragon Warriors on Ik-Soo's recommendation, becoming the first member of her group. He cut Yona's long hair short after she attempted to use an axe. As the primary non-combatant in the group known as the Dark Dragon and the Happy Hungry Bunch (or Happy Hungry Bunch), Yun serves as the indispensable caretaker, handling cooking, medical treatment, logistics, and strategy. His intelligence and resourcefulness frequently guide the group. He forms a sibling-like bond with Yona and becomes integral alongside Hak and the Dragon Warriors. During the search for the Seiryuu (Blue Dragon) Shin-Ah, Yun was captured by the Hakuryuu village guardians and imprisoned before being released upon recognizing Yona and Hak. He later expressed frustration over the rivalry between Hak and the White Dragon Kija regarding Yona's protection. His medical skills become increasingly vital, and his ambition to master medicine intensifies after encountering widespread suffering. When Yona later forms an uneasy alliance with King Su-won to address external threats to Kouka, Yun adapts. He befriends the court physician Min-Soo and assists Hak in seeking treatment for Su-won's terminal Crimson Illness, applying his medical knowledge. Despite lacking supernatural abilities or combat prowess, he compensates with practical skills, including creating explosives when necessary. His journey reflects development from a self-reliant orphan distrustful of the world to a valued member of a chosen family, dedicated to healing others and expanding his knowledge for the kingdom's betterment.