Mana pathways are a pseudo-nervous system that spreads itself throughout the human body and are what qualifies a person to be a mage. Along the pathways are mana gates, specific points that connect the material world to the astral plane. These gates are activated by a mage's life force through spells, allowing one to convert life energy into magical energy. The number of gates a mage has is determined at birth, with an individual's power depending on the number of gates they have. The amount of gates that a human being can contain are restricted by the limitations of the human body. However, there is a way for a mage to increase their power through external means that allows them to gain access to a larger amount of mana gates with no added risk to themselves.
Within each male sperm cell is a microscopic organism known as animalcule, a complete preformed individual representing miniature versions of human beings. These preformed humans develop and enlarge into fully formed human beings through the process of conception and birth. Magecraft allows individuals to bypass this convoluted process to create life in order to create a perfect servant loyal to its creator, known as a homunculus. These homunculi are grown within a specially built cauldron designed to hold magic brews. This brew is filled with various ingredients, such as eye of newt, as well as other lay ingredients, such as cow intestines and the seed of the mage in question. The resulting "child" emerges from this concoction as a fully grown adult, bound to obey its master's commands. Although they are intelligent, homunculi lack free will and individuality, making them the perfect servant.
As they were born from magic, Homunculi are immortal and physically difficult to destroy. As such, they are lack the limitations of the human body. This allows them to contain as many mana gates as their master wills or can afford, allowing them to achieve levels of magical power that human beings are incapable of. These mana gates are created artificially, and inserted into the body of the homunculus in a similar way to an organ transplant in a human. However, while they are more powerful magically, there are limitations to that power. While human beings are varied in the kinds of spells they can use, homunculi are limited to one specific spell at a time. These mana gates are infused with the power of an individually spell before they are placed within the homunculus, and must be swapped in and out as needed. This design flaw is unintentional, as most mages agree that they are better served with their creation being as diverse as possible. This forces beings like homunculi into areas of specialization, limiting their uses and preventing mages from maximizing them to their full potential.
The more magical a creature is, the more restricted its range of magic. How can this be the case?