Kurogane Kazuki is a high school student who has always prided himself on his unyielding physical strength and straightforward, blunt approach to life. He believes that any problem can be solved with enough force and determination, a philosophy that has earned him the nickname "Kurogane" (Iron) and a reputation as the school's toughest fighter. His world is turned upside down when he meets Saijō Mitsuki, a petite and seemingly fragile girl who transfers into his class. Despite her delicate appearance, Mitsuki possesses an extraordinary and terrifying psychic power: the ability to manipulate the emotions and memories of anyone she touches. This power makes her the "strongest" in a way that completely defies Kurogane's understanding of strength, as she can defeat any opponent without throwing a single punch, simply by making them forget their will to fight or by implanting overwhelming fear.

The initial conflict arises from their diametrically opposed natures. Kurogane, who solves everything with his fists, is both fascinated and frustrated by Mitsuki, who can resolve conflicts with a mere touch. Mitsuki, for her part, is exhausted by her power, which has isolated her from others due to the fear that she will accidentally erase or alter the feelings of those close to her. She is drawn to Kurogane's incorruptible honesty and his complete lack of fear toward her, as his sheer stubbornness seems to make him partially resistant to her abilities. The story follows their reluctant partnership as they are drawn into a series of conflicts within and outside their school. These range from protecting other students from bullying gangs to confronting rival psychics who seek to exploit Mitsuki's power for their own ends. Each confrontation forces Kurogane to adapt, learning that brute force is not always the answer, while Mitsuki begins to trust that her power can be used for protection rather than just as a curse.

A notable early arc involves a former classmate of Mitsuki's who was driven to madness after his memories of her were accidentally erased, leading him to form a group of disgruntled psychics who want to strip her of her abilities. This arc forces Kurogane to fight without his fists, relying on strategy and his unshakable will to get close enough to Mitsuki so she can use her power safely. Another significant narrative thread explores the origin of Mitsuki's powers, revealing a secret government research project that created her and several others. This leads to a confrontation with a shadowy organization that wants to reclaim her as a weapon, pushing Kurogane to confront the limits of his physical strength against opponents who can manipulate reality itself. Throughout these trials, the central relationship evolves from wariness and irritation to a deep mutual respect and burgeoning romance, as they each come to define "strength" not as a singular attribute, but as the courage to protect what is important despite one's own weaknesses. The story culminates in a final battle where Kurogane, having fully accepted Mitsuki's power and his own limitations, helps her achieve complete control over her abilities, allowing her to choose her own future rather than being defined by her past as a tool.