Characterized by white hair, red eyes, and black horns. The King of the Demon Realm who possesses immense power and authority. Initially treats the High School Girl harshly but gradually comes to understand and care for her. He is a long-time rival of Zeras. He is playful but can be serious when needed. He likes the High School Girl and takes good care of her. He maintains a close relationship through a contract with her. He hides the fact that he is a demon. He acts like a tsundere and is occasionally violent.

A senior one year older than the High School Girl. An honor student with excellent grades who is trusted by teachers. He comes from a wealthy family as the son of a National Assembly member. He shows interest in the High School Girl, forming a love triangle with Alpher. There is a plot point where he is taken to the Demon Realm due to Zeras's brainwashing. He likes the High School Girl and is in a contractual relationship with her. He calls her "High School Girl."

Alpher's long-time subordinate and loyal aide. Characterized by long red hair and green eyes. In the human world, he disguises himself as the High School Girl's English teacher. He can use powerful magic and moves according to Alpher's orders. He hides his identity as a demon. He is currently active as an English teacher. He calls Alpher "Demon King." He calls the High School Girl "High School Girl."

Alpher's pet who can transform into a dog. She has liked Alpher since childhood. Her affection for Alpher is a major relationship element in the story. She calls the High School Girl "High School Girl" and Alpher "Lord Alpher." She addresses most people except the High School Girl with honorifics. She is at the bottom of the Demon Realm hierarchy.

The rival of Demon King Alpher and a major antagonist from the Demon Realm. Rather than relying solely on strength, he pressures opponents through strategy and brainwashing. He intervenes in the human world by kidnapping the High School Girl and brainwashing Mobeom-saeng. He can transform into a cat. He calls Alpher "Demon King." Although he is polite, he treats humans recklessly with the goal of sealing Alpher away forever.

The main antagonist who has bullied the High School Girl for a long time. She vents the pressure of getting into a prestigious university and academic stress onto the High School Girl (though she doesn't extort money). She likes Mobeom-saeng and feels jealous of the High School Girl. She gains demonic power through a contract with Zeras but meets a tragic end.

The student council president who belongs to the top tier of the school hierarchy. One of the major school characters in the work. In the latter half, a plot point emerges where she goes with Zeras. She shows interest in Alpher. She is Rank 1. Her father is a National Assembly member.

A large-framed 2nd-year male student. He is close to Iljin-nyeo and likes her. Initially, he participates in bullying the High School Girl but shows an inability to actively exercise violence. Later, he takes reckless actions to try and bring Iljin-nyeo back. He is Rank 2.

A student with a thin physique. He is weak against those stronger than him but violent toward weaker students. Later, he enters into what appears to be a contract related to the demon Vina. In the latter half, he begins dating Lucy. He is Rank 3.