Content warning for themes like body horror, parasitism, medical horror, coercion, and harm to children.

Magic

Magic comes from a fungus-like organism that fuses with the spine of the host.

Its spore slowly dissolves flesh until it reaches a spinal disk. From there, it takes root using the nutrients from the host. As it grows, its structure slowly starts to deteriorate the spine, replacing it after a while. The stress on the nervous system, as well as the resulting malnourishment, led to a shortened lifespan. However, once the fungus reaches the nervous system, it produces enzymes that allow the use of magic. About two weeks after infection, the host is able to shove or pull mass telepathically. Usage of magic strains the nervous system but also strengthens the ability to use it.
It typically does not take a lot of training to surpass human muscle strength, and once the fungus replaces the spine completely, the magic becomes as potent as it can get.

Timetable:	Effect:	Curability:
Immediately after infection	Spore makes contact with flesh, adheres to the surface and begins to release enzymes to dissolve it	Yes, through cleaning
12 hours after infection	Spore reaches the spinal disk	Yes, through minimal surgery
24 hours after infection	First roots start to build	Yes, through minimal surgery
48 hours after infection	Roots invade the spinal disk, anchoring to it	Yes, through surgery
72 hours after infection	Fungus reaches the nervous system	Yes, through surgery
1 week after infection	Growth starts to be noticeable as a bulb on the back	Yes, through surgery
2 weeks after infection	The host starts to be able to manipulate environment telepathically	Yes, through invasive surgery
1 month after infection	The spinal disk is completely replaced by the fungus; growth breaks the skin	Yes, through invasive surgery
3 months after infection	Growth reaches the size of 20 cm	Yes, through invasive surgery
5 months after infection	Growth reaches maturity, spores are released	No
2 years after infection	The spine is replaced by fungus	No

*As the process is dependent on external factors such as temperature, abundance of nutrients, immune reactions of the host, etc., variability is to be expected.

There have been recorded cases of infections not reaching the spine but the limbs. In such cases, the growth is observed to occur stunted; no magical abilities were observed within the host.

Optimized growth has been observed when the humidity is relatively high; 60% seems to be the optimum for unrestricted growth. Temperature is a more variable parameter, although a higher temperature yielded better results than a lower one. The best results were achieved in a temperate climate, between 22°C and 28°C. Slightly acidic medium is seen as the most suitable to cultivate the fungus in experiments.
Adjusting these parameters allows accelerated growth, with some hosts reaching the final stage of their infection (replacement of the spine) within 1.5 years.

A method that was sometimes used to empower mages was the “Rose procedure," a surgical intervention where mages modified the frontal lobe of the patient, causing them to become less aware of the strain the use of magic placed on their nervous system, making them more likely to use it.
It also impacted the risk calculation, making the subject braver. These people brought havoc to the enemy faction. A spiral or rose-shaped indent marked the people who were modified.
The procedure is viewed critically by those affected.

In the past, it was common practice to select the children of potent mages and forcefully infect them with the fungus to create forceful and obedient soldiers. Many mages had their children taken away from them, and in turn, many of them did not know their parents. Only government-approved mages were allowed to raise their own children or decide about their infection status at all.
This practice was later lessened, mostly thanks to the efforts of a particularly strong-willed magic user who was not ready to give her offspring up. Even after her death, she is still said to haunt those who harm children.

The magic itself could mostly be described as a telepathic force. Its pressure creates spiral-like indents; only very controlled magic created even surfaces. The shape was a natural result of energy flow manipulation; the mage had to focus on a single point from where the energy would spread. The closer the gaps, the cleaner the surface.
With a lot of practice, some could create heat. Mages could easily be identified by the plant-like growth from their spines. From the top of it, spores were released, potentially spreading the infection itself. While many mages cut the blossom to avoid this, it was said to strengthen the magic to leave it as is.

Typically, mages were malnourished. This had two common causes: Either they grew up with the parasite that caused this form, or they decided to get infected to improve their living situation and compensate for poverty-related conditions such as prolonged starvation or illness. Infected military members often enjoyed privileges such as secure housing and easier access to food for themselves and their family. About 5 percent of the global population were infected people.

Many mages lived in temperate climates during the early stages of their infection, leading to "hotspots." These were typically in big cities, creating communities of magic users where many lawbringers were stationed. Nations with more extreme climates still relied on infected soldiers, the slower growth rate bringing a significant disadvantage. To compensate, partnerships emerged to trade resources. Some nations tried to work around this by employing new methods of warfare.
Within the deep north, early prototypes of firearms can be seen, while hot climates start to invest in the exploration of fungicides.

Warfare

In a world where direct confrontation of enemy forces was even more likely to end in death, war was often decided by the use of biological weapons. This included the infestation of drinking water with parasites. A common one was a leech that laid its eggs in the windpipe of its host, damaging its lungs with its waste products. If untreated for too long, the victim suffocated within a month.
Countermeasures such as water filtration were deployed but not always reliable, so drinking water was often disinfected by making some brand of alcohol out of it. Healers and medicine became quite important in confrontations, especially antibiotics, which were decisive in the prolonged survival of the soldiers.

Warfare generally focused on weapons with a long reach. Bows, crossbows, spears, and pikes were among the usual arsenal of soldiers, law enforcers, and guards. Bludgeoning weapons were also often used, mostly on battlefields where heavy armor could be expected. Swords were somewhat rare, although not unseen. Most of them were light; mass area denial was achieved by mages.

Religion

No matter if one is killed by the effect of a parasite, crushed to death by a magic user, or simply starves, death is unavoidable. And with this inevitability comes the attempt to rationalize this with religion.

The most common one was about the concept of the Core, the middle of the earth where everything goes in the end. It is the amalgamation of everything that was, creating gravity by its almighty pull. Once something dies, it can no longer resist this pull, and after years of being pulled down, it fuses with it. There, it becomes part of the one consciousness. Whether this is viewed favorably or not is dependent on the culture. Some see it as an honor, believing that the Core decides the destiny of the world by its collected wisdom.
In other cultures, becoming one with the core is suffering, becoming part of a crowded mass, endlessly pulled and pressed in the form of a perfect piece.

The distinction impacted many aspects, such as burials, matters of speech, and punishments.
Cultures that believed in the fast descent would typically bury the dead. The deeper the body, the more favorable the deceased has been viewed. Burials were a ritualistic digging; the more people cared about the dead person, the deeper the hole.
On the other hand, cultures believing in the slow descent would lay stone slabs under the body; sometimes entire crypts were built to halt the inevitable.
Depending on the culture, the saying “May you never reach the core” could hold very distinct meanings.

Depicting the Core was forbidden in some regions, although many temples included circle and oval shapes in reference to it. It was typical to see temples and churches build from stone and metal. Materials from the surface like wood as well as windows were generally avoided.

Neither side permitted the destruction of the body. Doing so was either seen as preventing the dead from reaching the Core or dramatically accelerating the travel to it. It was seen as a fate only deserving to the vilest of humans. Bodies of the enemy were often treated as neutral as possible; the usual compromise was a shallow burial to not attract scavengers.
Both believed that once the core becomes big enough, it hatches and destroys the world as known to bring a new one, born from the collective consciousness of its pieces.

Some cultures had a very different spin on the Core, seeing it as the mother of all. They believe in the idea that the core brought life into the world by laying eggs, each species in a distinct one. Once one goes back to the core, one becomes an egg again, bringing a new species in the new world once the core hatches.
As fatalistic as the religion of the core was, it also came with few obligations. Believers were expected to submit to the church and trust their judgment, but with no perceived deity came no rules to be enforced.

Few and far between was a shunned religion that believed in the “Great Leviathan," the world devourer. It is believed to be an immortal being, once only as big as an ant. As it lives, it eats. And as it eats, it grows larger. Its growth is the limiting factor of the world, because once it grows big enough, it will consume towns, cities, and entire nations. Until nothing else is left and it devours the world itself. Some believers say it’s aquatic, and some claim it to be terrestrial.
This faith is ancient; the followers of the Great Leviathans were often declared barbarians by the faithful of the Core. The idea that there would be anything bigger than the human will was seen as blasphemous.
Generally, this faith was rarely tolerated. This was caused by cultural differences such as their burial rite, including the burning of the body to slow the Great Leviathan's growth, and the religious belief in a life without reproduction. The followers were encouraged to adopt children instead of creating them. Whenever a child goes missing, some suspicion is typically put on the faithful of the Great Leviathan.
While them kidnapping children was something that could happen, the actual chances were very low; the suspicion was rather prejudiced than rooted in reality.

Myths and Legends

Outside of religions, myths and legends spread. They included creatures like the "Friend," who was said to only be seen by children in particularly bad situations. It is completely silent, only listening to them, never talking back. After a while, the children who see this creature just disappear, never to be found.
Another myth is about a poisonous toad. In a small dose, its poison is said to bring prophetic visions. This belief grew to people coming to the conclusion that the toad itself was able to see the future, making it a common pet of generals, kings, and other people who make important decisions. When the pet owner made a severe mistake, it was not unlikely for them to blame the toad for it in court, causing some instances of amphibians being executed for perceived treason instead of their human handlers.

Fiction was also impacted by the world around it. Many legends, stories, and songs romanticized the idea of a short but impactful life. The idea of the fungi giving everyone the means to defend themselves and change the world around it was often talked about. To compensate for a short life, a large family tree was seen as an option to secure one’s legacy beyond death. Infertile people were pitied but, in some instances, given a unique opportunity. If infertile couples were compliant enough, they were chosen as the adoptive family for mages children.
It was also said that the fungus positively impacts the fertility of its host. Depending on the context, this was either a misunderstanding or a lie.

Nature

Nature was harsh. A higher amount of oxygen led to bigger insects and creatures. Especially in cold regions, mammals could reach considerable heights. Many animals were highly specialized in their environment, creating a high variability in each region. Curiously, only very few creatures with fungal infections were observed, and none of them seemed to possess the expected telepathic abilities.
Domestication of plants and some prey animals allowed bigger yields while the taming of predatory creatures increased mobility.