Yakumaru Itsuki, codenamed Ya-kun, operates as part of the Scavenger mercenary group in Academy City. She conceals her striking features and long brown hair beneath a loose square-neck blouse, black spats, and an oversized brown newsboy cap, adopting a deliberately tomboyish aesthetic to deflect scrutiny. Her utility belt holds vials of specialized chemicals and spherical containers for triggering rapid reactions in battle. Combining sharp seriousness with a mischievous streak common to Scavenger members, Yakumaru executes missions with clinical precision, eliminating targets without hesitation and harboring deep disdain for authority figures—particularly teachers, whom she blames for systemic corruption stemming from implied past trauma. Her unwavering loyalty centers on her teammates, especially Leader, whose strategies she intuitively predicts during operations like their clash with Misaka Mikoto. Her esper ability, Mix Master, manipulates liquid specific gravity to separate or fuse chemicals, enhanced by custom compounds: flash-freezing coolant, 4,000°C liquid thermite, explosives, adhesives, and corrosive solutions. She crafts painkillers, deploys shock-inducing spheres, and employs tactical deception, such as faking a poison gas leak to manipulate Skill-Out evacuations. First active during the Necromancer Arc, she spearheads Scavenger’s annihilation of DA, overseeing headquarters destruction and confirming target eradication before Anti-Skill confrontations. Her thermite assault fails against Accelerator, who exploits her dependence on ranged chemical mixing to defeat her. In the Dream Ranker Arc, she tracks Kuriba Ryouko’s robotic doppelgänger, adapts to its resilience, and collaborates with Misaka under Leader’s orders, using theatrical deception to control Skill-Outs. Later, she pressures clients to reclaim Scavenger’s rank. During the Jailbreaker Arc, she covertly assists Misaka in the Second Reformatory crisis, disabling security drones and navigating operational errors like misidentifying target structures. Her keen observation captures nuances like Shirai and Saten’s interactions, which she misreads as flirtation, underscoring her situational awareness amid occasional tactical misjudgments. Her trajectory emphasizes combat adaptability, ruthless pragmatism, and allegiance to Scavenger’s survival within Academy City’s underworld, prioritizing contractual goals and team cohesion above all.