Homunculi are powerful magical beings with the power to reverse casuality and to manipulate magic with much more ease than humans.
They are created solely by Skull Mask.
The first prototype homunculus was created over 300 years ago and was a frankenstein-esque monster of mismatched human parts stitched together. The most recent homunculus created was the one to appear in the battle of Lagrium Plains and took the shape of a human girl with white hair and red eyes. While homunculi were simply created and used as humanoid weapons by Skull Mask with little personality to speak of and only followed orders and logic, the homunculus that appeared in the battle of Lagrium Plains displayed emotion, suggesting that they may have evolved enough to feel or fake human emotions.
It is unknown whether humonculi have the capacity for gender expression.