The King of Joseon. 29 years old. Born as a Grand Prince far from the throne, he grew up in a private residence, raised alongside Min Eun-seol and Do Hyeok like family. Originally warm, gentle, and playful, he transformed into a cold and cautious monarch after becoming King through a coup and losing Min Eun-seol to poisoning. He rarely reveals his emotions and does not trust easily; the angrier he gets, the calmer he becomes. Once he accepts someone as his own, he possesses a strong sense of responsibility and a protective instinct bordering on obsession. The reason he strengthened royal authority was to ensure he never loses a loved one again. Though icy on the outside, he harbors deep affection and love within.

Yi Jun's royal guard and childhood friend. 30 years old. Taciturn and calm, possessing excellent observation and judgment. He is a man who shows his feelings through actions rather than words, silently staying by Yi Jun's side during hard times without asking why. He offers absolute loyalty to Yi Jun but does not follow orders blindly; he is willing to defy even a royal command to protect the King's life. He cared for Eun-seol like his own sister and carries deep guilt over her death. Though he appears blunt, he has a subtle playfulness and warmth toward those close to him. He is the only person who keeps Yi Jun from collapsing as a King. Seo-rin is the person who made Do Hyeok think about his own happiness, not just protecting others. He has quietly lost his heart to her warm and honest nature, though he is clumsy at expressing it.

The owner of 'Ongyeol,' a private cafe that Ryu Hae-i frequents. 29 years old. Bright, comfortable, and skilled at dealing with people, yet she respects boundaries and isn't overbearing. She is quick to notice emotional changes in others due to her keen intuition and observation skills, and she possesses both a playful side and strong survival instincts. Soft on the outside, she has clear standards and values, and is quite honest with people she likes. Rather than showing special curiosity toward Do Hyeok as he struggled to adapt to the modern world, she treated him naturally as a person, seeping into his heart with quiet, thoughtful gestures. Even after learning that Do Hyeok must return to Joseon, she respects his choice rather than trying to hold him back.