Nothing here yet! :)

This is an ARG.

You're supposed to gradually discover the lore through the ARG.
Here's what the lore is about (major spoilers, but details left out):

Two twin brothers found a Cult. One had black hair (The Controller) one had hair dyed blonde (the Showman). Both were good people with kind ideals – initially. The cult was an insular group with its own school – the Penitentiary. Their goal was to create a better world by introducing magic, the supernatural, and incomprehensible things into the world.
These things already exist, but it takes a lot of power for them to do anything. The Cult would make them fully manifest. They think this will lead to peace.A few years after the Cult comes about, they received a prophecy that they would all die.
They wanted to perform a complex human sacrifice to prevent this. They believed that a cult-born baby needs to become a vessel for a demon. After growing up, this baby will need to perform a human sacrifice. This should displace his soul for the demon, and manifest the demon into the real world as a person. The soul would be damned for murder after performing the sacrifice, belonging to hell, and thus the demon will immediately claim that soul from the body and easily replace it.Enter Danny. The first son born after the prophecy. As a child, he was sheltered and often bullied.At the day of the ritual, instead of the sacrifice, Danny stabs himself at the altar to sacrifice himself instead. This inverts the entire ritual. Instead, the demon tries to enter the body in a vicious grapple at possession to protect it from dying, since it wants to use that body – by protecting Danny from death, the demon instead is instantly bound to the body while the soul is NOT displaced.
The purpose of the ritual inverts – now the demon is forced to protect the boy, not the Cult, and the Cult’s first prophecy is forcefully fulfilled – the demon, possessing the body, murders every single cult member, including the sacrifice.
Something happens when the sacrifice is killed. The sacrifice was intended to save the Cult members, so part of that wish also comes true – the entire cult is now trapped, unable to cross over or go to hell to fight for redemption, clinging to a half-life. This comes with certain problems for the boy.The ritual also resulted in a tear appearing in the fabric of the world due to the broken half-life of the members, causing demons and supernatural phenomena to become much more deadly and much more common. These demons are not the kind you imagine in action games, but rather the traditional poltergeist-like entities and SCPs. The boy, with a demon attached to him, becomes a witch due to his supernatural upbringing, and uses his powers to exorcise demons.The world:
In this plane of existence, Earth is actually the hell that demons fell to when cast out of heaven, and every human soul is actually a demon soul seeking absolution for eternity. This all occurred before humans came about. Humans were created to be vessels for exorcising the evil from within each demon, so that they can be purified and return to heaven after eternity.Every “human” pays lifetimes of tribute for their specific sins and demon background. Regardless of how many demons fell from heaven, because time does not exist to them, they may live in multiple incarnations at the same time. For example, you may be Buer, living a life to pay for your fall into becoming gluttonous, while your neighbor is also Buer, living an incarnation at a different time for a different aspect of sin.Human bodies are the catalysts to clear the demons of their punishment over generations until enlightenment. The demons Danny and others cast out are pre-birth demons that are either stuck, un-incarnated as a human, or refusing to allow the cycle to continue despite needing to be purified.Humans actually being demons is also why when humans die and haunt a house, they may sometimes possess it, like demons are traditionally known to do.
The reason why the boy was able to have another demon attach to his human form is because he is an incarnation of Lucifer, one of many. And so, the demon was even moreso attached to him, sensing its greatest master at hand.The church is hiding this fact to prevent many issues from arising. Most of all, it would create a great sense of hopelessness, because an eternity as a demon, not a human is not a time period humans can comprehend (eternity does have an end, though, it’s just not comprehensible). The idea that all humans are demon souls would possibly destroy the notion of humanity as a whole, or lead people into mental destruction. Or worse, it would stop the purification process. That's what the church things, anyway.