This is from my fanfic called Just a Country Boy in ASOIAF.
Now remember that everything about a Homo Arcanum was mostly made by me, and I did take inspiration from some things like Mana Circuits from Fate and other things, so keep that in mind.
Also keep in mind that I didn't just make this for my fanfic—I made it because I was bored and I thought that this was a unique and cool idea for a new branch of human, so you are all free to use it however you want to, and you are free to change some things about it too as you wish.
Homo Arcanum
The basic idea of a Homo Arcanum is that they are a branch of the human species that has evolved due to being exposed to mana for so long that it started to infuse itself into the nervous system and slowly into the whole body.
Now you may be wondering how that makes any sense at all.
The reason why the mana infuses into the nervous system is due to the fact that the whole body is covered in nerves, and that our nerves are the main reason why we feel pain, cold, heat, and other things. Also, they are the reason why we feel the things that we touch.
So I took that fact and assumed that the reason why we feel mana is because of the nerves.
Now evolution is a very weird thing due to the fact that almost anything can happen depending on the place where they are and how they are living.
Homo Arcanum evolved with innate mana control and an arcane nervous system (ANS) integrated into their physiology.
So there are three core features to the Homo Arcanum that I made.
Mana-Core Brain
Now this is a need-to-have for the ANS due to the fact that the mana-core brain is what helps the ANS properly.
Let me explain: the mana-core brain acts both as a biological processor (aka like our neurons) and a mana engine (aka like a magical reactor).
There are three main functions.
The first one is mana conversion, so basically it draws mana from the environment or internal reserves, then it turns it into safe and stable mana for the body to use. This process happens subconsciously in small amounts.
The second one is what I will call intent translator, so this is a little hard to explain well in a long explanation, so I am going to dumb it down a bit. So think of yourself as a Homo Arcanum and you are looking at something that is very far away from you—your body will read that intent of yours and it will direct mana into your eyes in a way that makes it so you see better. Now I know that explanation is kind of shitty, but that is the best way that I can put it so it makes sense.
For the last one, it is Mana Distribution Control—basically it works with the Arcane Nervous System (ANS) to regulate mana flow, send precise amounts to specific body parts like the legs for speed, arms for power, and so on, and this also prevents overload by balancing intake/output.
Let's talk about the physiological benefits of having the mana-core brain. There are many of them, but I will only talk about the main three. The first is cognitive enhancement, so basically you will learn faster, have better memory, better thinking speed, and so on. The second one is emotional-mana link—now this one can be both a benefit and a downside because think of it like this: you are doing a fire spell while you are boiling with anger, so the fire spell will come out stronger and hotter, but it will also be wilder and more aggressive. And then there is the sensory expansion that focuses on mana—like you can smell traces of mana a little bit.
Now there are risks and weaknesses that come with the mana-core brain, but I will talk about two of them that are really important to know about. The first one is mana burnout—so if you process too much mana at once, then you can fry or crystallize your neurons, and that would cause seizures or death.
Arcane Nervous System (ANS)
Now this, in the most simple terms, is a mana-supercharged version of the nervous system.
I was going to make it like it was a parallel network in the body of a Homo Arcanum that is alongside the biological nervous system, but I decided not to do that and make it so it is a better version of the nervous system.
Let's move to the functions of the ANS.
Mana conduction: the ANS channels mana from the mana-core brain through the body to specific regions in almost instantaneous response to one's intent.
Body reinforcement: when mana floods into muscles, bones, or skin via the ANS, it strengthens them depending on how much you want it to. Now the reason why it floods mana into everything in that specific area is due to the fact that if you only put mana into your arm, then the muscles and everything else will break, so the ANS puts mana into everything in that specific body part and related to it so you do not hurt yourself at all.
Sensory overclocking: when you flood or extend mana into the sensory organs, then they will become superhuman-like depending on your intent—like if you were to intend to see something moving, then mana will get sent into your eyes in a way that it locks onto the things you are looking at in an eagle-like way.
Reflex enhancement: the ANS carries mana-infused electrical impulses that are way faster than normal electrical impulses. These mana-infused electrical impulses act nearly instantaneously, so you would be able to dodge arrows, react to attacks faster, and other things, and there are also normal electrical impulses.
Spellcasting conduit: now mana doesn't always stay in the body. The ANS directs it out of the body through the skin, eyes, mouth, or hands. The hands and fingers are especially rich in ANS endings, making them ideal channels for spells. Also, it allows you to easily channel mana into weapons to make them stronger.
Structure of the ANS: the primary channels are thick mana nerves along the spine connecting brain to core body. Secondary channels are the branches of nerves that run alongside the veins and muscles. The tertiary filaments are the delicate strands that weave into the sensory organs and fingertips for precision.
Weaknesses for the ANS: Overload—forcing too much mana through the ANS can cause "mana burn," scorching nerves and disabling mana use temporarily. Disruption—certain toxins, curses, or anti-magic fields can sever or paralyze mana flow. Dependency—just like nerves, damage to ANS strands can cripple abilities—e.g., losing precision in spellcasting if finger filaments are damaged.
Physiology of Homo Arcanum
Now because the nerves have mana in them and how nerves are in every part of the body, technically mana does leak from all nerves into the whole body in small amounts.
Let's start with the skeletal system. Bones did evolve into having mana-conductive minerals that make the bones slightly denser than a Homo sapiens. Due to that fact, the bones resist fractures and even self-repair minor cracks. Now the joints are reinforced by mana, so that reduces wear and tear on them. Also, the growth plates stay active longer, so you will grow taller and more flexible.
Muscular system: all types of muscle fibers are naturally more elastic and dense. They are capable of channeling mana directly into contraction. Tendons are woven with micro-mana filaments that act like springs, storing and releasing energy. Basically, if you go to throw a proper punch, it will have way more force behind it even when not using mana.
Circulatory system: the blood of a Homo Arcanum contains mana plasma that carries mana alongside oxygen and nutrients. The heart pumps not only blood but also mana pulses syncing with ANS. The circulatory system has higher oxygen running through it, so a Homo Arcanum has greater stamina, faster healing, and other things.
Respiratory system: the lungs have expanded alveoli density (aka meaning that there is more oxygen intake per breath), can hold breath for very long durations, can filter some toxins and gases, and can also breathe thin air at high altitudes with mana.
Digestive system: can convert food into both nutrients and mana-fuel. Can eat some things that would get other people sick with no effects at all.
Sensory system: now I don't think that I really have to explain this one, but I am going to add some things that I didn't say earlier. All the senses are stronger due to all the nerves that they have already, even if one is not overclocking them with mana (aka making them stronger and better). The senses are better than a normal Homo sapiens.
Immune system: the whole system is reinforced by mana, making it so Homo Arcanum are resistant to most natural diseases, and they can adapt immunity to new pathogens through repeated exposure.
Reproductive system: fertility cycles are partly influenced by mana saturation. Offspring inherit mana capacity genetically, though strength varies. Pregnant Homo Arcanum unconsciously feed developing children with mana, boosting early resilience, and also the semen of a Homo Arcanum is way stronger than a Homo sapiens.
Aging and longevity: the mana in the body causes slow cellular decay, causing Homo Arcanum to live way longer than a Homo sapiens. Homo Arcanum will look youthful longer than a Homo sapiens.
Traits That Are Visible
Now this part you can skip if you want to, but I would not really recommend it.
This is to show the visible traits that Homo Arcanum have that Homo sapiens don't have.
Eyes: a Homo Arcanum's irises will shimmer faintly when mana flows. That color is different for each person. When casting a spell, the pupils or sclera may glow in low light. The eyes of a Homo Arcanum will appear more too clear, too vivid—like polished crystals—even when not using mana.
Skin: when under stress or heavy spellcasting, faint glowing lines of the ANS may show beneath the skin. The skin of a Homo Arcanum will heal cleaner—scars fade faster and their skin will look perfect with no marks, no scars, or anything like that. Their skin also appears brighter and healthier.
Hair: Homo Arcanum hair is often vibrant. Also, when a Homo Arcanum overuses mana a lot, then the hair will slowly bleach itself or turn silver.
Veins: now when a Homo Arcanum uses mana, then their nerves will faintly glow—like if you use mana in your arm to punch, then that arm will glow faintly.
Posture and movement: Homo Arcanum are unnaturally fluid in their movements—like how they move is too balanced, like that of a predator or a dancer. Their reflex speed is uncanny in timing.
Senses and expressions: they react to distant or faint things—like they turn their heads to a direction where they hear something, or they would sniff things to smell the scent. Their sensory organs are sharper—like how a Homo Arcanum staring at you feels more piercing, or how their listening looks more focused.
General vitality: they appear younger than they are. They let out a subtle aura of health and energy due to the fact they are very rarely sick and skin is often flushed with vitality. Then their presence feels intimidating or captivating to Homo sapiens.
The Uncanny Valley of the Homo Arcanum
A Homo Arcanum looks too "perfect" compared to a Homo sapiens—like they look too healthy, their skin is too smooth, eyes too sharp, posture too balanced.
Believe it or not, our brains subconsciously notice the flaws in the looks of a person we meet. It is a wired behavior that we have in our brain because in all reality we are fucking animals that have just gotten lucky and are smarter than others. Anyways, as I was saying, a Homo sapiens will notice that a Homo Arcanum has no tiny scars, blemishes, or imperfect balance because we are aware that we have that deep in our brain, so it's normal for us—but then comes a person with none of that, so it will bring some uneasiness or discomfort from staring at something human but too perfect-looking to be human.
Did you know that our brains make it so that we get mad or really nervous when we are looked at for too long?
Because that behavior is animalistic, and the reason why I am bringing that up is because the gaze of a Homo Arcanum tracks things at an unnatural accuracy, and a gaze like that will make a person feel like they are being weighed, measured, or pierced.
A Homo Arcanum's body naturally leaks faint mana, and a normal non-mana-using Homo sapiens cannot sense mana, but their nervous system can react like they are near a strong electromagnetic field or wild predators (aka heart rate quickens, adrenaline spikes slightly, hairs on the back of the neck rise).
Another thing about Homo sapiens is that their expressions are not as fast or smooth as a Homo Arcanum, or how a Homo Arcanum's eyes will flicker to a sound before a Homo sapiens even hears it, to which a Homo sapiens notices that subconsciously, and that small difference will make a Homo Arcanum feel alien in a way.
Side Notes
Now you are able to change anything in this as you wish, and I really don't care if you do, but my only advice if you do change something—then make the change that fits into the rest of it.
I did make sure to take into account the biology aspect into this because I have read fanfics with Biokinesis and they use the whole power wrong if you ask me—like if you are going to make the bones stronger and denser, then you have to make the muscles and tendons stronger and better too, or you might fuck up your limbs, or how they make their heart stronger, then they will have to make the blood vessels stronger too, or they will get messed up.
Anyways, Homo Arcanum are humans—just a "better" version of them—and they give Homo sapiens an uncanny valley feeling.