The story begins with Mitsuba, a silver-haired, blue-eyed girl with pale, doll-like skin, awakening from a ten-year vegetative state in the mansion of Duke Gilmore Blue Rose Clove. Suffering from amnesia, she possesses fragmented knowledge of a "previous world" (TV, smartphones) and struggles to understand her current reality. Her father, Gilmore, a doting and overprotective Duke, is overjoyed, revealing Mitsuba is the keepsake of his beloved first wife, Tsubaki (an "Onmyoji" from a foreign land), and is destined to inherit the Blue Rose name.
Mitsuba quickly learns her prolonged survival was due to Gilmore's immense wealth and the Royal Magic Research Institute's use of "magic light stones" and "catalysts." She discovers her stepmother, Miliane, and two half-brothers, Griel and Miguel, with whom Gilmore has a deeply strained relationship, living in a separate annex. Maids and the butler, Pierre, are terrified of Mitsuba, believing she can "suck souls," a fear exacerbated by her unsettling, expressionless demeanor.
Gilmore, increasingly frail and paranoid, bestows upon Mitsuba the Blue Rose Staff, performing a "soul engraving" ritual to bind it to her and protect her, muttering darkly about preventing "harlots" from inheriting. Meanwhile, Miliane, a cunning and ambitious woman from the Yellow Rose family, plots to seize control of the Blue Rose house for her son, Griel. She uses Pierre as a spy and spreads malicious rumors about Mitsuba being a "cursed doll" who killed her mother and is now afflicting her father.
At a party intended to unveil Mitsuba as his heir, Gilmore collapses, poisoned by Pierre under Miliane's orders. As he dies, guests whisper about Mitsuba's curse. Mitsuba, detached but with a fleeting moment of tears, bids her father "Goodbye." Miliane quickly assumes the role of acting head, announces Griel as the future heir, and has Mitsuba confined to an isolation tower. Pierre is found dead the next day, poisoned, leaving Miliane with a fleeting suspicion.
In the dark, moldy tower, Mitsuba's boredom leads to the discovery of her unique, destructive abilities. She accidentally causes a guard to collapse and later disintegrates magic barriers and chains with a touch, emanating a toxic purple light. Her unsettling presence and the gruesome deaths of guards and staff lead to widespread terror and reinforce her "cursed doll" reputation.
Nikolaynas, the eccentric and brilliant director of the Royal Magic Research Institute, intervenes. She reveals Gilmore's death was due to illness and poison, not a curse, and that Mitsuba is a "high-explosive shell" with immense, unpredictable power, capable of returning malice with malice. Nikolaynas, who helped Gilmore "create" Mitsuba, refuses Miliane's demand for execution, fearing catastrophic consequences. Instead, she suggests sending Mitsuba to the Roselia Royal Army Officer Academy, specifically the unpopular Artillery branch, to "disperse her malice" on the battlefield.
Mitsuba, eager to escape boredom and learn about this new world, agrees. She is enrolled as "Mitsuba Clove," her honorary Blue Rose surname temporarily stripped. At the academy, she meets the stern Artillery instructor, Gard, and Krone, a cynical, tall, messy-haired former noble who becomes her first friend. Mitsuba, still naive but with a growing awareness of her power, chooses Artillery for its "destructive power" and "fun to shoot" aspect, much to the horror of the academy headmaster, Paluck. The story concludes with Mitsuba, no longer a passive pawn, embarking on a new path, a dangerous and unpredictable force in a turbulent world.
