Carry On, Wayward Sons [Harry Potter's Brother Reader]

Demonology

As Y/N arrived at his lesson with John, he entered the room and saw Winchester cleaning his weapons.

"Hey kid. How you been?"

"Good but busy." Y/N said as he looked at John.

"Keeping up with little brother so I hear." John said as Y/N chuckled.

"Yeah. I brought the book from the library that you told me to, Pince nearly threw a fit." Y/N said as John laughed to himself as he imagined Y/N having to negotiate with Pince.

"Bet that took some work getting Pince to hand that over." He said as Y/N nodded. 

"You could say that." Y/N said as he revealed the large book, with gold rimmed pages, the gold having faded as Y/N looked at the cover of the book.

Demonology: A Compendium of Evil and Combatting It

"I'd like you to take note of what I'm about to say and over the next few days I'll be asking you to illustrate these notes, given how the best way to ensure you never forget how to combat a threat is to illustrate it and give you a visual memory." John said as he looked at Y/N. "Ready?"

"Yes sir." Y/N said calmly.

John nodded calmly before he spoke.

"Demons are the result of human souls going to Hell and being tortured until no humanity is left in them, thus turning into demons - dark, malicious spirits that revel in pain, chaos, and death. In general, demons engage in torture and destruction because it is fun or to avoid being tortured themselves. Some demons, however, are true believers in Lucifer's agenda to "cleanse" Earth, and actually consider themselves morally superior to humans.

There are many ways of becoming a demon, from making a deal with a Crossroad Demon, to being a witch, and making a deal with another demon. They manifest on Earth in the form of a long, slender cloud of black smoke.

Once a soul becomes a demon, it gains the basic demonic powers (possession, superhuman strength, etc.) and from there, it can work its way up the ladder to positions of greater authority and power within Hell. Often when a demon has used its powers, they leave a trace of sulphur in the nearby space, or if on a person, around the victim. This can give away the demon's presence, indicating to hunters that they are hunting a demon. Very powerful demons leave much more sulphur than average. Some demons are sent back to Earth to accomplish certain tasks, such as causing disasters, spreading diseases, assassinating hunters, or manipulating people into committing crimes that will get them sent to Hell. To do this, they have to take a vessel or "meatsuit" in order to physically exist. While nearly all demons desire to escape Hell any chance they get, some demons actually prefer Hell.

When they possess humans, they usually enter through their mouths. On one occasion, a demon entered a human via the eyes. Possessed humans often look exactly the same as they did before possession, the only noticeable change being that their eyes will sometimes change colour (black, red, white, grey, or yellow depending on the demon possessing them). Demon possession also causes a chemical change in the circulatory system of the host; demon blood is known to be a unique serum and has certain attributes when ingested. Whenever they use their powers, they leave a trace of sulphur in the form of yellow dust.

Often under possession the human begins speaking and acting like the demon would. Upon exorcism, the human—if they survived—retains no memory of their time during possession (unless they have been "awake" during possession, in which case the time of possession is a nightmare for them, literally). The possessed humans also gain the powers of whichever demon is possessing them. Unlike angels, whose possession of a human vessel has to be with the vessel's consent, demons forcibly possess humans. People suffering from stress, fear or panic can be vulnerable to demonic possession. Demons abhor the name of God (Christo), and will flinch and reveal the vessels black eyes if it hears the word.