Yumiella Dolknes, a reincarnated Japanese college student, discovers at age five she's the villainess of the otome game "Light Magic and the Hero." Her goal is a quiet life, but her black hair makes her an outcast, even to her parents who send her to their territory alone. She soon realizes she's the game's secret, overpowered boss, capable of dark magic. Driven by a gamer's spirit, she spends years secretly leveling up to 99 in monster-filled areas, developing immense physical and magical abilities, including infinite mana.
At 15, her father orders her to the Royal Academy. Her black hair immediately draws prejudice. At the entrance ceremony, her level 99 is revealed, shattering her hopes for anonymity. She's instantly accused of cheating by the game's main capture targets: hot-headed William Ares, second prince Edwin Balshine, and cool-type Oswald Grimzard. Yumiella, frustrated, tries to redirect them to the heroine, Alicia Enlight, a light magic user who has already befriended the princes and glares at Yumiella.
In sword class, Yumiella, despite never using a sword, effortlessly defeats William. In magic class, she melts a reinforced target with a small dark flame, shattering Oswald's pride. Edwin attempts to expel her, but Yumiella, after getting him to take responsibility, demonstrates her power by casting "Black Hole," plunging the academy into temporary darkness and terrifying Edwin.
Summoned by the King, Yumiella proves her strength by effortlessly dodging the kingdom's strongest knight, Adolf. The King and his mage subtly rehabilitate dark magic and black hair, which are typically associated with evil. Yumiella, desiring a peaceful life, rejects the King's offers of immense rewards and royal marriage, stating she will be the kingdom's "shield." The Queen later reveals the Demon King will revive in two years, asking Yumiella to assist but not personally defeat it to preserve royal legitimacy. Yumiella deflects the "Saint" role to Alicia and rejects royal marriage. The Queen warns her of political factions, including Yumiella's own family's extremist allies, and offers protection, which Yumiella uses to fend off recruitment attempts.
Alicia then publicly accuses Yumiella of being the revived Demon King, citing her black hair and dark magic as "proof," based on a state secret Edwin carelessly revealed. The capture targets side with Alicia, their pride shattered by Yumiella's strength, leading them to believe she's evil. Yumiella, exasperated, tells them to get stronger to fight the *real* Demon King.
The new Headmaster, Ronald, a perceptive royal liaison, confirms Yumiella is the cause of the capture targets' instability. During outdoor training, Yumiella, bored, uses a monster-calling whistle. Patrick Ashbaton, a pragmatic frontier noble, takes charge, leading efficient group combat. Patrick is injured protecting Yumiella, who panics, uses "Black Hole" again, and heals him with grotesque Dark Heal. Patrick, genuinely concerned, scolds her for her recklessness. This marks the beginning of a genuine friendship. Patrick, once self-conscious about his own dark-ish hair, respects Yumiella for embracing her true self. Yumiella realizes her game counterpart might have hidden her dark magic, leading to her villainess path.
From an isolated villainess seeking anonymity, Yumiella's overwhelming power forces her into the spotlight, disrupting the game's plot. While she gains political allies and a genuine friend in Patrick, the main characters become deluded enemies, setting the stage for a complex future where Yumiella must navigate her role in saving a kingdom that simultaneously fears and needs her.
