Name: Ryusei Narukami A mathematics teacher at Mitsurugi Girls' High School, characterized by black hair with red streaks and glasses. His true identity is the deadliest "Demon King" who attempted to destroy the world in his previous life. While he lived as a shut-in NEET in his past life, he has completely changed since reincarnating into the modern era, working diligently and earnestly wishing for a peaceful, stable daily life. However, his peace has already crumbled because Meteor, the former Hero who followed him to this school, stalks him daily and picks fights by force. His former majesty is nowhere to be found; in the modern world, he occupies the position of a long-suffering man pushed around by Meteor and his former subordinates. Despite his cool and detached attitude, he has a kind nature and ends up looking after his students anyway.

Name: Meteor Kaori A high school girl characterized by long pink hair and colorful streaks. In her previous life, she was the "Hero," the strongest human who saved the world, boasting overwhelming combat abilities. Even now, reincarnated in modern Japan, she simply loves fighting and shows an abnormal obsession with the Demon King (now Ryusei Narukami), with whom she fought to the death. She forced her way into the same school just to trade blows with him again, and even breaks into his home, leading those around them to mistake her actions for passionate romantic advances. The line between "intent to kill" and "affection" in her feelings for Ryusei is blurred. She is a reckless and incredibly cute former Hero who hides the ultimate destructive power behind an innocent smile.

A cheerful and energetic high school girl belonging to the track and field club at Mitsurugi Girls' High School. Her trademark is a large red ribbon tied in her ponytail, and she carries a boyish, approachable atmosphere. She is a mood-maker who leads those around her with her natural brightness and outstanding initiative. She is a character who purely enjoys modern high school life. However, her high physical abilities and her occasional flashes of straight-laced, passionate justice mesh well with the story's fantasy-like incidents, and she unknowingly gets swept into the vortex of the strange relationships between the former Hero and Demon King.

A high school girl serving as the class president of Class 2-2, which Meteor and the others attend. She is a beautiful girl with tan skin, long blonde hair, and intellectual glasses. She is highly capable as a class leader, earning deep trust from those around her as a calm, collected, and disciplined person. At first glance, she appears to be an ordinary modern person unrelated to the feuds of the past life, but she is actually a reincarnated person who retains strong "memories of the past life." Her true identity was the mysterious "Strategist" who supported the Demon King's army from the shadows, and in this life, she plots to support her former master, Ryusei, behind the scenes. She has a gap between her public face as a clean-cut class president and her cold-hearted side as a strategist. She also dislikes men.

A high school girl in Meteor's class with striking long blonde hair. In her previous life, she was a "Demon General," one of the Four Heavenly Kings of the Demon King's army who served the Demon King (now Ryusei Narukami) with absolute loyalty. Even after reincarnating in modern Japan, her overwhelming adoration and loyalty to the Demon King have not faded at all, and she struggles day and night to be of use to Ryusei and to elevate him to the position of King of the World once again. She and the former Hero, Meteor, have been arch-enemies since their previous lives, and they clash fiercely in this life over Ryusei. While she usually appears to be a gentle, soft-spoken beauty, she possesses extreme initiative—stopping at nothing for the Demon King's sake—and the pride of a demon, making her a very devoted character with a charming gap.

A high school girl and classmate of Meteor. Her true identity is the strongest "Holy Knight (Grand Knight Captain)" who fought alongside the Hero Meteor against the Demon King's army in their previous life. In this life, she also has clear memories of the past and acts to support and protect her beloved Meteor from the shadows. She is generally serious, polite, and plays the role of the voice of reason who stops the others from running wild. However, she becomes extremely overprotective when it comes to Meteor and often casts a harsh gaze at Ryusei, the former Demon King who jerks her around. While showing glimpses of her high combat skills and mental strength as a knight in modern school life, she navigates the hectic school days with deep loyalty and friendship for Meteor.

A magical girl who wandered in from a parallel world. She is serious but perhaps a bit short-tempered? She has a very responsible personality but can be surprisingly quick to anger and prone to jumping to conclusions. Upon arriving in this world, she completely misunderstood the high school teacher Ryusei Narukami to be the "mastermind who caused the dimensional rift" and suddenly attacked him. She transforms into the magical girl "Asahi," and the gap between her quiet everyday appearance and her fierce, dangerous combat style is her main charm.

Ryusei Narukami's younger sister. A high school girl characterized by long brown hair and a flower hair ornament. She used to treat her brother coldly when he was a shut-in NEET, but since he returned to society and became a teacher, she treats him normally. Although she is usually harsh with him, she cares for him deep down. She also has a side where she witnesses their slapstick antics at the perfect (or worst) timing and misunderstands the situation.

A student at Mitsurugi Girls' High School. Originally gloomy, she is a "Returned Hero" who came back from another world with cheat abilities. She manipulates skills like Charm and Appraisal and has a dangerous side where she chooses any means to achieve her goals. Seeking magical power to return to the other world, she targets Ryusei as a foil/rival heroine.

In her previous life, she was the Princess of the Kingdom of Runeberg. A mysterious girl who holds the key to the story, whom Ryusei served as a court magician before he became the Demon King.