Black allows Shihai to merge his body into anything that is black-colored and move himself through it freely.
Shihai can blend with any object that's dark-colored by nature or due to external conditions, such as shadows. The ability does not appear to take in account mass, so merging with small or thin black objects, such as a mushroom or a cape, is entirely possible. This Quirk is most efficient in cramped areas with little to no lighting, where shadows are abundant and the lack of space physically hinders those Shihai ends up fighting or escaping from.
Objects that are naturally mobile can be forced to move if Shihai manages to assimilate into them. Because of this, Black holds an advantage against Dark Shadow, a dark-colored living appendage, which he is capable of possessing and then controlling its actions regardless of Fumikage's wishes.
Brightening up a shadowed location will quickly leave Shihai cornered, forcibly ejecting him from any non-black object if the shadow shrouding it vanishes. As such, it has a weakness to light-based Quirks.
It also appears that Shihai can keep the ability "on hold" while looking for something black to merge with, which an enemy may exploit by forcing his body into an black object they are able to grasp (which prevents Shihai from leaving).
Shihai originally could only merge himself with black objects, but after strengthening his Quirk, he is now able to move the incorporated black objects themselves, although those objects need to be mobile in the first place.
In combat, Shihai uses Black to hide from enemy attacks or to execute ambushes. Once merged with a black object, Shihai can move through its whole structure at very high speeds, even while carrying a person.
- Black appears to function similarly to Mimicry, although it has some key differences:
- Black is limited to objects which display a certain color. Mimicry does not have this limit.
- Mimicry is limited to objects of a certain size, smaller than a refrigerator (larger objects could only be possessed through the effects of Trigger). Black seemingly does not have this limit.
- With Mimicry, Joi could manipulate the object he was currently possessing in any way he wanted, changing even its shape. Shihai had to improve his Quirk first before being capable of doing so, and even then, he's limited to manipulating only mobile objects into moving.
- Since Black and Dark Shadow are darkness-based Quirks, they share the function of being more effective in darkness, as well as the weakness for being less effective when exposed to light.