Hell and Nightosphere Connection
Sometime after Lucifer and Lilith became king and queen of hell, Hunson's father took the opportunity to establish business connections between the Nightosphere and Hell. This included the construction of an Abadeer estate built in the second ring of Pride as well as trading of different kinds of goods such as materials, drugs, etc.
The Rings
Hell is divided up into 7 rings with each ring ruled by one of the seven sins with the only exception being with the Pride Ring. Each ring has nine "circles", different areas of the ring where different cities reside. While fallen angels, higher ranked demons such as the goetia and hellborn can travel to all 7 rings as they wish, sinners can't.
Pride Ring: The first ring. It's ruled over by Lucifer (king of the hellborn) and Lilith (queen of the sinners). The Pride Ring is primarily red in color and it's surrounded by mountains. Sinners are restricted to this ring but can inhabit the nine circles of Pride.
Wrath Ring: The next ring. It's ruled over by Satan. The Wrath Ring is primarily orange in color and is a volcanic desert. All imps hail from Wrath, where most end up running farms to provide food for all of hell.
Gluttony Ring: The third ring. It's ruled over by Beezlebub. The Wrath Ring is primarily yellow in color and filled with endless jungles. All hellhounds originate from Gluttony. While Wrath provides most of the food, the Gluttony Ring provides most of Hell's drinks and sweets.
Greed Ring: The 4th ring. It's ruled over by Mammon. The Greed Ring is primarily green in color and full of huge cities that pump out pollution. Greed is the provider of a majority of Hell's financial system. The Loan Sharks (hellborn demon sharks) originate here. Organized crime is common here and cops tend to turn a blind eye to it (this is Hell) as long as don't affect Mammon directly such as stealing from Greed's banks.
Lust Ring: The 5th ring. It's ruled over by Asmodeous. The Lust Ring is primarily blue in color, constantly raining, and full of buildings with neon sings. Lust provides a majority of good related to sex from toys to full size sex robots. Succbi originate from here and are one of the few demons with the natural ability to enter the human world. In addition, the Lust Ring also has Asmodean Crystals, magical minerals that allow hellborn to access the human world.
Envy Ring: The 6th ring. It's ruled over by Leviathan. The Envy Ring is primarily purple in color and has an ocean theme. Infestors and other hellborn fish demons originate from here with Infestors being one of the few demons with the natural ability to enter the human world. Envy Ring is the fashion district of hell.
Sloth Ring: The 7th ring. It's ruled over by Belphegor. The Sloth Ring is primarily pink in color and surrounded by clouds and waterfalls. Baphomet demons originate from here with most becoming medical practitioners (doctors, surgeons, therapists). Sloth Ring is Hell's medical center; Hell's hospitals and rehab centers are all located her and Hell's prescription drugs originate from here.
The Exterminations
500 years ago, Lucifer and Lilith gave birth to a baby boy, Damian Morningstar. It wasn't long until the higher-ups of Heaven found out about the new prince of Hell. They viewed Damian as a threat; someone who could lead Hell into an uprising against Heaven. So they had Damian taken from his parents and approved the exterminations.
While the sins, Goetia, and the Morningstars knew of that the exterminations were to stop hell from rising against Heaven, most of hell were told that the reason for exterminations were because of "overpopulation" in the Pride Ring. And given that no one was really sure what got you into heaven, the lower class demons believed in "overpopulation" reason. While most hellborn are able to leave the Pride Ring, some imps and hellhounds don't often have the same luck and will try desperately to either remain in their homes during extermination or try not to be seen by the exorcists at all. Despite the hellborn being pardoneded, that didn't stop Adam and the exorcists from killing a few imps and hellhounds alongside hundreds of sinners.
The Goetia
The Ars Goetia are demon royalty that were created by Lucifer (didn't initially like the idea that Lucifer created them but it grew on me). Aside from Paimon, there were 8 goetia kings/queens. While some were related to each other, not all of them were which allowed them to have their own family lines, making the goetias what they are today. For the most part, the goetia dukes and princes are those who were given actual roles in hell such as Stolas being given the job of studying earth's skies. Arranged marriages are very common with some marriages being decided when a goetia is a fledgling. While the LGBTQ+ are generally accepted in hell, the LGBTQ+ amongst the goetia is...a bit more nuanced. While some members might be more accepting of those in the LGBTQ+ (with some of the goetia being LGBTQ+), some of the more older members of the goetia weren't as accepting (with exceptions).
Winners
Winner angels are the counterparts of sinner demons; once human souls who ascended to heaven when they die. Like sinners, winners can't age and can only be killed by angelic steel. In addition, winners are capable of possessing unique powers such as Carol's (Serena's mom) magic singing ability that could influence someone's emotions. Winner angels can also grow in power such as Adam, one of the first winners, who ended up becoming an archangel. While some exorcists are heavenborn angels, some exorcists are winners who signed up to join the exorcist army and as such, were some of the very few winner angels who were aware of the exterminations. While winner angels are much more fertile than sinners, there are rules in place that unless you're in a higher social circle, winners are not allowed to procreate and can be punished by being cast down.
Cherubs
Cherubs are the counterparts of imps. Much like imps, cherubs are the lowest class in Heaven and make up Heaven's workforce. Aside from being assistants to higher class angels and doing manual labor, a lot of cherubs work at C.H.E.R.U.B., a non-profit organization that sends cherubs to earth in order to protect humans on behalf of ascended souls.
Sinsmas and Christmas
Both Christmas and Sinsmas are holidays celebrated in hell.
Sinsmas is a hellborn holiday. It's basically the same as it's celebrated in Sinsmas; depending on the ring you were born into, you celebrate the sin of that ring. For example, those from wrath often celebrate sinsmas by brawling or those from gluttony get wasted or gorge on food. But as hellborn started going around other rings and mixed hellborn started to rise, some hellborn just decided to celebrate whatever sin they wanted.
Christmas is a sinner holiday. It's basically celebrated the same as it would be on earth, just minus all of the religious stuff as this is hell.
As hell began to grow and sinners established their place in hell's social heirarchy, some of their christmas traditions began to rub off on the hellborn's sinsmas (decorated trees, giving presents).
Heaven Holidays
The heavenborn have their own version of sinsmas (virtuemas???) where you basically celebrate whatever virtue you want. Like for charity, the heavenborn would do deeds in order to help those in need.
Similar to the sinners, the winners also brought their christmas traditions up to heaven but since this is heaven, the religious aspects of christmas are much more prominent.