Hong Gildong is a young boy born to a nobleman and a lowborn servant in 15th-century Joseon. Blessed with high intelligence, physical strength, and mastery of magic and divination, he deeply resents the rigid class system that prevents him from pursuing a noble career or even calling his father "father." Despite his youth, he possesses a strong moral compass and an overwhelming ambition to prove himself as a true man in society.

State Minister Hong Mo is an illustrious nobleman in the capital city of Jangan. As a highly respected former state councilor, he values tradition, family reputation, and loyalty to the king above all else. He finds himself deeply conflicted by his illegitimate son's extraordinary talents, torn between his paternal love and the societal pressure to suppress a lowborn child who might disrupt the social order.

Chunseom is a nineteen-year-old servant in the Hong household who belongs to the lowborn class. Despite her status, she maintains a gentle, proper demeanor and a respectable character. As a mother, she worries about her son's safety and desires only that he accept his place in society to avoid causing trouble, reflecting the harsh realities and lack of autonomy faced by female servants in Joseon.

Chorang is the senior concubine in Minister Hong's household and a former courtesan from Goksan. She enjoys a position of great influence as the minister's favorite but remains frustrated by her inability to conceive a child. Bitter and arrogant, she regularly spreads rumors about those she dislikes and views the young boy and his mother as direct threats to her status, driving her to plot drastic measures to eliminate them.

The King of Joseon serves as the supreme patriarch of the nation. He represents the country's strict laws, traditions, and the intersection of filial and sovereign loyalty. The king values merit and capable leadership but operates strictly within the rigid class structures of the era, making him both a distant, revered authority figure and an indirect enforcer of the limitations placed on lowborn citizens.

Hong Inhyeon is the legitimate son of Minister Hong and his wife, working as an assistant section chief at the Ministry of Personnel. He embodies the traditional, successful nobleman path that his younger brother desires but cannot pursue due to birth status. Though he cares for his sibling, Inhyeon remains intensely loyal to his family's reputation and his country's laws, forcing him to choose between filial duty and familial affection.

Teukjae is a local assassin operating in Joseon. Driven primarily by money rather than morality, he takes on violent assignments for wealthy patrons without questioning the ethical implications. His involvement with the Hong family serves as a critical test for his target, forcing a confrontation that challenges the boundaries of martial skill and moral philosophy.