This Quirk 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 a refrigerator, but when his Quirk is boosted, presumably by the drug Trigger, he is capable of manipulating entire locations.
Joi mostly uses his Quirk to inhabit a small, black cloak, which he uses to move around and interact with others. He is also capable of manifesting his real body parts from an object he is possessing.
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.