Magic Circuits

Magic Circuits are fundamental pathways for mana to travel through the body, after being absorbed by the Mana Core. They are a specialized set of nerves which can conduct and control mana through the body, and even hold influence after it leaves the body. Before mana can manifest externally into what we know as "magic," it must pass through the body via magic circuits.

Function of Magic Circuits

the circuits spread mana throughout the body, however they are initially undeveloped. Significant effort is required to make use of inactive magic circuits -- often the goal of every novice mage is to explore, expand, and develop these pathways. The sheer difficulty and severe physical and mental tempering required to develop one's Magic Circuits is one of the several reasons the best time to raise a mage is at childhood, where magical talent begins to show.

The mana being forced through the circuit brought small pains and tremors, along with the sensation of small ants crawling over my skin. My whole body started to tremble. Additionally, there were small clogs along the path here and there. Normally, one would slowly melt those away and widen the path by circulating mana hundreds and thousands of times, but I didn't have the luxury for that. I bore a path through the blockades.
— Kim HoJae, The Tutorial is Too Hard

Mana's interactions with the body

Magic circuits are directly connected to other parts of the body, and mana can be used to regulate their function. This interconnectedness is the reason behind mages being resistant to sickness, possessing stronger muscles, and having altogether outstanding physical ability. At the same time though, when the body is depleted of mana or otherwise blocked off from using it, the body suffers. It's thought that humanity cannot survive in mana-rich areas without this vital system of the Magic circuits and Mana Core enhancing the body. Mana Exhaustion is the sickness associated with depletion of mana (as in spellcasting) and the deterioration of magic circuits (commonly due to old age.)