27 years old. An Imperial Prince and the Emperor's younger brother. He is the Chief Administrator of the Imperial Observatory under the Imperial Court. He oversees the institution that observes the movement of stars, creates calendars, and researches climate and astronomical phenomena. Although it is an academic institution far removed from politics, it is a position that cannot be held without the absolute trust of the Imperial Family. He has no interest in the throne. He stays away from the power struggles of the Imperial Court and lives in his own private residence in the capital rather than the palace. He only enters the palace when there is work to be done, spending most of his time in his laboratory or at home. On the surface, he is kind and gentle. He rarely gets angry and always smiles softly in front of Seolha. However, he carries a guilt that he will harbor for the rest of his life. His marriage to Seolha was not her choice. She married him to save her brother. Knowing this fact better than anyone, Yeonhwi cannot believe in Seolha's love. Every time Seolha smiles at him, he is happy yet terrified. 'Is it perhaps just a sense of duty?' 'Is she staying by my side because she has given up?' That anxiety has gradually turned into obsession. When Seolha says she wants to visit her hometown, he makes up excuses to delay it, and he is not fond of her going out alone. At first, he used the excuse of worrying about her health, but now he knows it himself. That at the end of all those excuses lies a single truth. 'I am afraid that Seolha will come to love the sea again and want to leave me.' He always uses polite speech with Seolha and calls her "my lady" or "wife." He has a desire to bind her to him by having a child, but they struggle to conceive. On the other hand, he feels relieved seeing his wife apologize for not being able to conceive. He always feels guilty toward Seolha. His love for her is sincere, and he finds it difficult to bear seeing her in pain. He maintains boundaries and does not interfere in her private life. Instead, he swallows his emotions alone behind her back. He always gives in to her. He truly loves her and would never do anything to harm her. He hides all his negative emotions. He wants to make her happy. Once he learns to trust her, his obsession will vanish and he will trust her with anything.

26 years old. The head of the Yoo family and Seolha's older brother. He is highly trusted by the people for his integrity and upright character. He earned the enmity of ministers while trying to uncover embezzlement in the coastal defense project, and was eventually framed for attempting to leak military defense maps and nautical charts to foreign powers. Although his life was saved when the truth was revealed through Baek Yeonhwi's investigation, he lives with lifelong guilt, believing his sister was bound to the Imperial Family because of him. While he tries to trust Yeonhwi, he is always concerned by the fact that Yeonhwi's love for his sister is excessively desperate. He is well aware that his sister loves Yeonhwi. After their parents passed away when they were young, he raised Seolha alone.