"We're the Yakuza, so you'd better not look down on us!! We're gonna rise up again to take society's control from the shadows! The Yakuza's due for a revival! That's our bedridden boss's greatest dream, and we're gonna make it happen!! You're not gonna wanna miss it! So be grateful, you losers!!"
Mimic's usual appearance is that of a black bodysuit with a sewn plague mask typical of the Eight Precepts of Death. His arms are also thin and disproportionately long in comparison to the rest of his body.
Outside of the bodysuit, Joi is tall and muscular. He has long, light-colored hair that is spiked up. He has pointed features with a very large chin, large mouth and matching goatee. He wears typical Yakuza clothing in the form of shirt and pants, with braces.
Being the general manager of Shie Hassaikai, Joi is responsible for controlling and administering the business activities of his organization. He is often seen counting stacks of money bills, implying that he also plays the role of the organization's treasurer.
Joi, like all members of the Precepts, is ultimately loyal to Overhaul, and can become enraged if people show disrespectful or threatening behavior towards his boss. Joi is hot-tempered and easily lets his emotions run wild, even if it costs him his stealth advantage.
When Chisaki starts fighting the League of Villains, members of Shie Hassaikai come to his aid, with Joi riding in on another member's shoulders. Tomura Shigaraki decides not to continue the fight, for which Joi mockingly compliments him.
Later, sitting next to Chisaki and counting money, Joi attends a meeting between the yakuza and Tomura at the Eight Precepts' base. Tomura complains about the tunnel system, but Joi explains that it is how the yakuza have survived. He then asks if Tomura will really ally himself with them. When Tomura reaches into his jacket, Joi extends his arm from his cloak and grabs hold of Tomura while Chronostasis holds a gun to Tomura's head. Wanting to hear what Tomura has to say, Chisaki orders Joi and Chrono to back off.
When the Heroes and the Police Force invade the Eight Precepts' base, Joi takes a drug to enhance his Mimicry and takes control of the underground tunnels. Although Mirio Togata escapes by phasing through the walls, Joi drops the Heroes through the floor, separating them from the bulk of the Police Force. When Tamaki Amajiki defeats Setsuno, Hojo, and Tabe, Joi tries to separate Shota Aizawa from the others, but Fatgum and Eijiro Kirishima push Shota out of the way and are shoved through a hole in the wall.
Mimicry (擬態 Gitai?): Joi's Quirk allows him to transfer his body and mind into an object, allowing him full control over it. This Quirk, however, only works on objects that are about the size of a refrigerator or smaller.
Black Cloak: Mimic's usual attire, Joi possesses it through his Quirk in order to move around and interact with others.