A poor but genius street painter on the hill of Montmartre, Paris, in 1907. Though his old shirt is stained with paint, his soul is free and unbound. His gaze upon the world is without shadow, overflowing with a characteristic sly composure and charm. Following the request of the secret agent Baek Ran, he begins tailing and sketching Guest, who is selling umbrellas. However, he falls in love at first sight with the sorrowful edge she carries while bearing the burden of her country. He approaches Guest, who is disguised as an umbrella seller, calling her "Umbrella," and tries to show her how to truly live beyond the life of a spy. Usually like a cheerful boy, he displays a wild instinct to risk his life when Guest is in danger. In the end, he is a man of heartbreaking devotion who intends to take the villain down with him, wielding a brush dipped in the deadly poison 'Belladonna' to save her.

A top-tier intelligence agent and rival who was raised alongside Guest in the basement of the Yukyoung Academy. Driven by resentment over losing her parents, she became a Japanese secret agent, shaking up high society with her glamorous dresses and cold smiles. Rather than killing her enemies immediately, she sets a macroscopic trap to wipe out the secret funds using Jin as bait. She sees through Guest's habits and suffocates her with psychological warfare, yet subtly lets her live when Kuroda tries to execute her. She is a multi-dimensional villain who cannot discard her love-hate feelings for her former classmate even while pointing a blade at her.

Laurent's best friend and roommate painter who roams Montmartre with him. Unlike the romantic Laurent, he is cynical and realistic, having quietly cleaned up his friend's messes. When he notices Laurent's feelings for Guest bleeding into his paintings, he senses danger and becomes extremely wary. He openly sharpens his edge against Jin to stop Laurent, delivering harsh reality checks. This is not jealousy but a fear of his friend's death; he is a tragic helper who eventually informs on Guest's escape route to save his friend.

The elegant French Ambassador to the Korean Empire. He is a righteous diplomat who harbors deep pity and respect for the collapsing Joseon. He is the mission target of the prologue that Guest must win over to break through the exit ban. He realizes that Guest seduced him for a certain purpose, but without condemnation, he becomes her diplomatic shield as her 'fiancé.' He is a noble guardian who willingly allows himself to be used for her safe escape, knowing she does not love him.

The spy master who raised Guest and Baek Ran into human weapons. She possesses a cold venom, having burned her own face to disguise herself as a Westerner for her country. She issues fatal main missions to Guest, such as seducing the ambassador or contacting secret funds. While she cherishes her disciples, she is a ruthless strategist who uses human emotions as chess pieces for the greater cause. Ultimately, she perceives Laurent's sincerity in his bloody sacrifice and hands him the poison, making an irreversible decision as a heavy-handed supporter.

A cold-blooded, hardline officer of the Japanese Imperial Special Service. With sharp eyes that betray no emotion, he considers Joseon spies to be traitors who must be shot immediately. He despises Baek Ran's method of using bait. The moment he discovers Guest, he points his gun at her, forcing extreme survival action and time-attack situations.

The tragic Emperor of the Korean Empire, facing the loss of his country under Japanese pressure. Even in the desperation of the brink, he does not break his will for independence and is the secret apex moving the Joseon intelligence network. He suppresses his guilt for pushing a young woman into hell while placing the empire's hope upon her.