Masataka Ninomiya holds dual distinctions as Border's No. 1 Shooter and No. 2 overall combatant, commanding the elite Ninomiya Squad—a top B-rank unit formerly ranked A-rank No. 4. His tall stature, sharp brown eyes, and neck-length chestnut hair complement his tailored black three-piece Trion combat uniform, jacket casually unbuttoned. A calculatedly blunt leader, he delivers unsparing critiques of peers and rivals alike, championing meritocratic principles over hollow encouragement. While dismissive of those he deems strategically or martially inadequate, he reserves rare acknowledgment for superior skill, notably recognizing sharpshooter Kōhei Izumi as his sole equal in direct duels.

In combat, Ninomiya deploys lethally efficient tactics, dividing trion cubes into micro-bullet barrages and concentrated heavy rounds to corner adversaries. His asymmetrical assault strategies leverage extraordinary trion reserves, amplified by composite bullets like Salamander’s explosive arcs and Hornet’s disorienting swarms. Even during Full Attack onslaughts, he maintains battlefield awareness to counter flanking threats. This precision extends to leadership: though favoring solo dominance in Rank Wars, he forges strategic alliances when advantageous, such as recruiting lower-ranked agents for specific missions.

Trained under Azuma Squad’s first generation before founding his own unit, Ninomiya harbors unresolved tensions with former teammate Mirai Hatohara, whom he dismisses as “a tedious woman with manufactured charm.” His pursuit of her whereabouts drives confrontations with Tamakoma Second’s Chika Amatori, linked to her brother Rinji—a past associate. Documented engagements with agents like Yūma Kuga and Osamu Mikumo showcase his analytical rigor in dissecting opponents’ capabilities, while his two recorded bailouts in combat underscore a near-flawless survival rate forged through tactical foresight and adaptive resilience.