A timid student named Fumio Kijima is living a miserable life, frequently suffering at the hands of bullies. His situation takes an unexpected turn when a girl who claims to be a devil from the demon world suddenly appears in his room. Introducing herself as a campaign girl for the demon realm, she grants Fumio an unusual supernatural ability: the power to summon a room out of thin air. Initially, Fumio is hesitant to exploit this gift, using it only for mundane conveniences in his daily life. However, his restraint ends when his classmates target him with an especially cruel and unfair act of bullying, pushing him past his breaking point. Vowing to make them regret their actions, Fumio decides to weaponize his power, beginning a campaign of confinement and brainwashing to achieve his revenge.

The central figure is Fumio Kijima, a previously passive victim who transforms into an active and ruthless antagonist as he embraces his darker impulses. The devil girl who provides him with his abilities acts as the catalyst for the entire story, though her true motivations remain ambiguous. The power she bestows is not a typical combat ability but the capacity to generate an extradimensional room. The exact nature of this room becomes the core of Fumio’s strategy, as he learns to use it to trap and psychologically manipulate his targets. The narrative is set in a contemporary Japanese high school environment, where the familiar backdrop of classrooms and student hierarchies contrasts sharply with the dark, isolated spaces of the summoned room where Fumio carries out his vengeance.

The story follows a clear trajectory from powerlessness to domination. The opening arc establishes Fumio’s victimization and his first contact with the devil girl, leading to his acquisition of the room-summoning power. A period of tentative and benign use of his ability follows, before the inciting incident of severe bullying pushes him to commit to a path of revenge. The central narrative thrust then becomes Fumio’s systematic retaliation against his classmates, as he learns the intricacies of his power and escalates his methods from confinement to outright brainwashing. The manga tracks his moral descent as he evolves from a sympathetic victim into a perpetrator, exploring themes of vengeance, power dynamics, and corruption. The work is authored by Masai for the story and illustrated by Ashimoto☆Yoika, and it has been serialized in the seinen manga magazine Young Dragon Age since September 2021.