Shizuri Mugino ranks fourth as Academy City's Level 5 esper, designated "Meltdowner." Her ability manipulates electrons into a state between particle and wave, generating high-speed particle-wave cannons. These destructive beams pierce and vaporize targets with extreme heat, can be shaped into shields or limbs, and are deployed with precise calculation. She began with four simultaneous beams, later expanding to twenty through training. To counter slow firing rates, she disperses beams into multiple projectiles using silicon cards ("Silicon Burn"). The power's inherent volatility requires constant subconscious restraint to prevent self-harm. Deliberate overload via the drug Body Crystal temporarily unleashes tens of thousands of beams at enhanced potency, followed by severe fatigue. After physical mutilation, she received prosthetics: a reinforced left arm strong enough to crush carbon weapons and a right eye with electronic surveillance capabilities. Beyond her esper power, she exhibits high resilience, enduring gunshot wounds and limb loss while continuing combat, and delivers potent physical strikes capable of inducing nausea or incapacitating large animals. Born into the globally prominent Mugino Family, one of the world's five wealthiest dynasties, her lineage profited from Westernized grain production while concealing criminal enterprises. Raised in distinct "darkness," her childhood included mentorship by butler Mujinayama and exposure to hybrid cultural practices like flower arrangement. Enrolled in Academy City at an unspecified time, her ability was cultivated within the Hula Hoop particle accelerator under researcher Ainame Caroline. She later rescued Takitsubo Rikou from false imprisonment intended for experiments, recruiting her as ITEM's inaugural member. Unbeknownst to Mugino, this aligned with Director Nakimoto Rizou's plans to test Level 5 creation methods via rival projects. As ITEM's field leader, Mugino coordinated mercenary operations in Academy City's "Dark Side" alongside Takitsubo, Saiai Kinuhata, Frenda Seivelun, and later Hamazura Shiage. Her leadership blended pragmatism with condescension; she praised competence like Hamazura's lock-picking skills but dismissed perceived liabilities, excluding Frenda and Takitsubo from battles against Misaka Mikoto. She exhibited protective instincts, visiting Frenda's grave and defending her legacy against impostors. However, vengeful obsession escalated during conflicts with rival faction SCHOOL. After SCHOOL killed ITEM allies and psychologically manipulated her, she murdered Frenda over perceived betrayal—an act that later haunted her. This triggered her descent into irrational vengeance, leading to ITEM's dissolution and her mutilation by Hamazura Shiage, who outmaneuvered her to protect Takitsubo. Losing her right eye and left arm, she replaced them with crude energy constructs and pursued Hamazura globally, abusing Body Crystal during battles in Russia. Her fixation manifested as drawn-out enunciation like "Haaamazuraaa" and self-destructive tactics. Post–World War III, Mugino underwent physical and psychological rehabilitation. Prosthetics replaced her energy limbs, with cosmetics masking most mechanical traces. She reconciled with surviving ITEM members, reforming the group as the only pre-war faction to persist. Her personality softened: she displayed patience with Last Order's antics and humor when confronted about her underwear, though violent outbursts against threats remained. She prioritized defending allies like Hamazura, Takitsubo, Kinuhata, and Frenda's sister Fremea Seivelun, whom ITEM collectively safeguarded. While acknowledging her capacity for killing and destruction, she expressed confidence in "happy endings" contingent on Hamazura's forgiveness. This redemption included accepting lower-level espers and rejecting former elitism. In spinoff material focusing on ITEM's early operations, she accepted a two-million-yen contract with the organization ATOM, reinforcing her underworld role prior to Hamazura's involvement. Chronological accounts from the "Enemy Item Arc" detail her participation in an underground fight club offering high-stakes financial rewards.