Joi Irinaka, alias Mimic, acts as general manager and treasurer for the Shie Hassaikai yakuza. He is a tall, muscular man with sharply pointed facial features: a spiked nose, a long square chin, and a notably large mouth. His relatively long blond hair stands spiked up, complemented by a matching goatee. He typically wears traditional yakuza attire—a dress shirt, pinstriped pants, and suspenders. When utilizing his Quirk, he inhabits a black bodysuit featuring short limb protrusions and a white plague mask sewn over the face position, serving as both disguise and mobility aid. In his role, Joi manages business administration and finances, often observed counting money during organizational activities. He displays fierce loyalty to leader Overhaul and the comatose boss, consistently voicing their goal of restoring yakuza power. This devotion ignites intense anger when others disrespect Overhaul or the organization's objectives. Joi possesses a volatile temper, leading to emotional outbursts that undermine his stealth effectiveness. His impulsiveness surfaces starkly during encounters with League of Villains members Himiko Toga and Twice, whose mockery provokes reckless decisions. Joi first appears atop another member's shoulders during Overhaul's confrontation with the League of Villains, arriving to support his leader. Later, he physically restrains Tomura Shigaraki during a strategic meeting after Shigaraki makes a sudden move; Overhaul intervenes before escalation. During the hero raid on the Shie Hassaikai compound, Joi ingests Trigger to amplify his Mimicry Quirk. Enhanced, he merges with and manipulates the entire underground tunnel network, strategically separating heroes and police by distorting corridors, creating barriers, and dropping adversaries through floors. His tactics successfully isolate key heroes like Eraser Head, Fat Gum, and Eijiro Kirishima. However, Toga and Twice deliberately taunt him about the Shie Hassaikai's fading relevance, provoking rage. Losing composure, Joi loudly vows to crush them, revealing his hidden position. Izuku Midoriya breaches his concealed location, exposing him. Eraser Head erases his Quirk, causing him to fall helplessly. Sir Nighteye incapacitates him with a Hyper-Density Seal, leading to capture. Even restrained, Joi shouts accusations of betrayal against Toga and Twice before police custody. His Quirk, Mimicry, allows him to transfer consciousness into inanimate objects for control and manipulation. Normally, he can possess objects up to refrigerator size. Trigger enhancement dramatically expands his range to entire structures like the underground labyrinth, but causes significant physical strain and reduces spatial awareness. To monitor surroundings while merged, he must manifest body parts externally, creating vulnerabilities. Official assessments rate his abilities as Technique 5/6 (A) and Wits 3/6 (C). Joi's equipment includes his signature black cloak—animated via Mimicry for mobility and interaction—and Trigger auto-injectors for Quirk enhancement during critical missions. His story involvement is confined to the Shie Hassaikai arc, with no appearances in subsequent arcs, films, OVAs, or spin-off media beyond his arrest.