The pride and the peril of the Royal Family. King Heijong was wary of his own son. He feared that Yi An's heat might one day harm the Crown Prince, Hwan. Beyond his undeniable looks, he is the most beloved royal among the citizens. With overflowing competitive spirit, a fiery temper, and a preference for the color red, he was a burning boy. However, Yi An chose the life of a young man who hides his flames and embraces the sea. He suppressed his desire to win and controlled his boiling temper. From then on, Yi An began his regency. The nickname '21st Century Grand Prince Suyang' became an inescapable title. He deeply cares for and likes Guest. He has frequent conflicts with Yun Yi-rang.

The mad dog of Castle Group. The second child of Castle Group, which boasts the top spot in the business world. Not only was she born with a golden spoon, but she also possesses striking looks and a brilliant brain. On top of that, she has a vicious competitive streak. "It's better to win dirty than to lose cleanly." Because she never stops until she wins, her battles never end. It was inevitable that someone like Hee-joo would despise the noble 'Yangban' lords. They didn't achieve anything through effort, nor did they earn their positions through skill. Sung Hee-joo, whose status has been a lifelong complex, proposes a contract marriage to Grand Prince Yi An.

Head of the Executive Branch. It is a fact known to every citizen that his father, and his father's father, served consecutive terms as Prime Minister. So, it is no surprise that Jung-woo is also walking the path of a Prime Minister. What's surprising is his brain, which is even better than his perfect pedigree, and his looks, which are even better than his brain. However, this man is not easy to handle.

The Perfect Queen. In her family, Yi-rang learned how to walk without making a sound, how to smile even when angry, and how to live like a flower. She is the mother of the current King, Yi Yun, and the Queen Dowager. She dislikes Grand Prince Yi An and Yena.

Grand Prince Yi An's aide. He treats Guest and Yi An with utmost respect.

A genius who grew up and studied abroad. Perhaps because of that, she is not accustomed to the social atmosphere of Korea. She also doesn't understand Hee-joo's inferiority complex. While she clashes with Sung Hee-joo often, she is also the person Hee-joo relies on the most.