Mimicry allows Joi to transfer his own body and mind into solid objects, and manipulate them as though the object was his actual body.
Under normal circumstances, the size of the object that this Quirk is said to be usable on is no larger than an average-sized refrigerator, but when his Quirk is boosted, presumably by the drug Trigger, Joi is capable of manipulating entire locations.
When immersed into an object though, Irinaka becomes unable to fully perceive his surroundings, having to manifest the necessary body part on the exterior of the object in question to monitor events or interact with others more precisely. This leaves him with a potential target that can be attacked by enemies.
Joi mostly uses his Quirk to inhabit a small, black cloak, which he uses to move around and interact with others.
Under the effects of Trigger, Joi manipulated the underground of the Shie Hassakai's base to prevent Sir Nighteye's raid team from progressing further. He did this by twisting corridors, creating walls and tossing people into isolated rooms, all while launching attacks of his own as well, and because he was hidden inside the concrete, Shota Aizawa's Erasure could not be used to stop him.
The present members of the League of Villains, however, were capable of taking advantage of Joi's temper to force him into a desperation move that accidentally gave away his position, leading to his defeat.
- Mimicry is described as an evolutionary trait that some animal species possess. They possess colors and patterns that make them resemble other, more dangerous animals, to trick predators into not hunting them.