Someone else did this not too long ago, but they got some details wrong, plus their post is like buried so I will be providing another one. Please reply with corrections and I will try to edit my post.
Ryujin and Imae Backstories: Ryujin was born with a disposition that attracts demons to try and posses him. A Shaman warns his family and tries to take him away, but the family refuses, so Miss Shaman warns them to keep him away from fire. Ryujin is plagued by demons (or specifically Sahon, the demon servant to one of the 4 demon generals) and that makes his family afraid of him so he is confined to a remote room. To keep himself from being afraid in his isolation, he lights a candle that burns his family and home to the ground. Miss Shaman comes back and tells him to go to exorcist school.
Imae, whose real name is unknown, was born to a mystic exorcist and mariner. However, since his mother is sworn to serve a local deity in exchange for her powers, she cannot have a relationship with her ex-lover and child. Imae grows up with his loving father who awaits the day when the 3 of them can be a true family. Imae only visits his mother when he needs help warding off demons who come to haunt him (because he has mysterious power??). One day while waiting for his father to return from a fishing trip, Imae witnesses a demon destroy his father’s ship, killing his dad. With no other family, he is sent to live with his mother, who gives him a small room in a shed and does not concern herself with him. One day when watching his mother cleanse water sprites, he sees the water sprites drag her underwater. He runs to save her and his mysterious powers exorcise the water sprites but also kills the village’s deity earning his mother’s scorn, costing him his name, and resulting in his being kicked from his village. He wanders the mountains alone for a year or so before meeting Ryujin (who was on his way to exorcist school).
Legend of the Mirror (Chapter 9): Immortals One lived on earth with humans, humans worshipped them and the Immortal ones became arrogant and their emotions created demons. God forced the Immortal Ones to go a space called “Heaven” while humans were confined to “Earth”, but were bestowed a “Sun Mirror” made of God’s Divine Power. Once the Immortal Ones were gone, the Four Demon generals attacked and broke the mirror, stealing some of the shards. There were still shards left with the humans, but the broken pieces of the mirror did not have enough power to act as a sun, warming the land, so a persistent winter arose. King Chan comes into power in the future and is visited by a divine Flaming Lion. King Chan then uses the remaining power of the mirror shards to perfect a sealing spell where he sealed the 4 generals (in the shards). 200 years later, the mirror is whole again and becomes the sun (again) bringing warmth back to the kingdom.
Note: King Chan did this with the help of five compatriots, who then make the five great exorcist families. Two of the known families are the Moon and Lee family (Bohyun’s and Hwan’s family)
20 years from the “present”, the First Attack on the Central Ministry of Exorcists: Part of the Seal on the Hall of Hidden Mysterious where all the sealed demons are kept breaks "mysteriously" and some demons escape (maybe this is how Sahon came to haunt Ryujin who is 20). Many exorcists die (including Bohyun’s brother Sihyun).
“Present”: Ryujin and Imae are accepted into the Central Ministry from exorcists school (even though they spent years failing), the first recruits in 20 years. Head of the Ministry is Taeryung (who we later learn is some half-demon/human being and is also a double agent in the Ministry). When the main duo get sent on a mission to visit the Gyeru Institute (which studies demons), Ryujin falls into a secret Immortal Ones portal (ch. 20/21), so now we learn there are some (few) Immortal ones trapped on Earth. When the mission is over, Ryujin and Imae are heading back home to the Ministry, but find it on fire (like it had been 20 years ago). Everyone is dead save Juwon (the exorcist with pink and cyan eyes and the chocker tattoo who would give Ryujin advice). We learn Taeryung’s true identity and that he was the one who partially broke the seal 20 years ago and completely broke it now. Current King/Emperor does not trust the Ministry or exorcists, so he blames the entire incident on them, which is why Ryujin, Imae, and Juwon are in hiding. Since demons are actively wreaking havoc, the king still must now rely on the 5 great families for exorcisms, so the Moon family is hiding the 3 ministry exorcists as king cannot touch them.
Four Generals: Geusendae- Shadow Demon (Sahon’s master the one who first proposed they break/steal the mirror) Daesun- Dream Demon (snake boi who is infatuated with Wudo, a demon who loves humans and works with the Gyeru institute [Wudo I mean not Daesun]) Kangchul- Steel Demon (first to agree with Geusendae because she believed the mirror would be the only way for demons to survive if the Immortals left Earth; a demon lover) Hojung- Fox Demon (betrayed demon kind and my theory is he became a new mirror to help King Chan seal himself and his “sibling” generals)
Wudo is a demon we first meet at the end of ch. 21 who introduces himself as a demon allied with the Gyeru institute. He says he loves humans which is why he lives with them and wants to fix the current never-ending winter that has fallen upon the kingdom. It seems Wudo and Daesun were lovers of sorts in the past, but when Wudo choose to interact and live with the humans, Daesun grew jealous and joined his siblings in destroying the mirror (the first time) in order to reclaim Wudo’s attention (it didn’t work as he planned).
Ryujin's Disposition: We learn that Ryujin's body is able to hold enormous amounts of Divine Energy (which is what demons and Immortal Ones alike need to survive). This is why Sahon has attached himself to Ryujin like a leech from birth (to get Ryujin's body as a vessel for Geusendae).
Someone else did this not too long ago, but they got some details wrong, plus their post is like buried so I will be providing another one. Please reply with corrections and I will try to edit my post.
Ryujin and Imae Backstories:
Ryujin was born with a disposition that attracts demons to try and posses him. A Shaman warns his family and tries to take him away, but the family refuses, so Miss Shaman warns them to keep him away from fire. Ryujin is plagued by demons (or specifically Sahon, the demon servant to one of the 4 demon generals) and that makes his family afraid of him so he is confined to a remote room. To keep himself from being afraid in his isolation, he lights a candle that burns his family and home to the ground. Miss Shaman comes back and tells him to go to exorcist school.
Imae, whose real name is unknown, was born to a mystic exorcist and mariner. However, since his mother is sworn to serve a local deity in exchange for her powers, she cannot have a relationship with her ex-lover and child. Imae grows up with his loving father who awaits the day when the 3 of them can be a true family. Imae only visits his mother when he needs help warding off demons who come to haunt him (because he has mysterious power??). One day while waiting for his father to return from a fishing trip, Imae witnesses a demon destroy his father’s ship, killing his dad. With no other family, he is sent to live with his mother, who gives him a small room in a shed and does not concern herself with him. One day when watching his mother cleanse water sprites, he sees the water sprites drag her underwater. He runs to save her and his mysterious powers exorcise the water sprites but also kills the village’s deity earning his mother’s scorn, costing him his name, and resulting in his being kicked from his village. He wanders the mountains alone for a year or so before meeting Ryujin (who was on his way to exorcist school).
Legend of the Mirror (Chapter 9):
Immortals One lived on earth with humans, humans worshipped them and the Immortal ones became arrogant and their emotions created demons. God forced the Immortal Ones to go a space called “Heaven” while humans were confined to “Earth”, but were bestowed a “Sun Mirror” made of God’s Divine Power. Once the Immortal Ones were gone, the Four Demon generals attacked and broke the mirror, stealing some of the shards. There were still shards left with the humans, but the broken pieces of the mirror did not have enough power to act as a sun, warming the land, so a persistent winter arose. King Chan comes into power in the future and is visited by a divine Flaming Lion. King Chan then uses the remaining power of the mirror shards to perfect a sealing spell where he sealed the 4 generals (in the shards). 200 years later, the mirror is whole again and becomes the sun (again) bringing warmth back to the kingdom.
Note: King Chan did this with the help of five compatriots, who then make the five great exorcist families. Two of the known families are the Moon and Lee family (Bohyun’s and Hwan’s family)
20 years from the “present”, the First Attack on the Central Ministry of Exorcists:
Part of the Seal on the Hall of Hidden Mysterious where all the sealed demons are kept breaks "mysteriously" and some demons escape (maybe this is how Sahon came to haunt Ryujin who is 20). Many exorcists die (including Bohyun’s brother Sihyun).
“Present”:
Ryujin and Imae are accepted into the Central Ministry from exorcists school (even though they spent years failing), the first recruits in 20 years. Head of the Ministry is Taeryung (who we later learn is some half-demon/human being and is also a double agent in the Ministry). When the main duo get sent on a mission to visit the Gyeru Institute (which studies demons), Ryujin falls into a secret Immortal Ones portal (ch. 20/21), so now we learn there are some (few) Immortal ones trapped on Earth. When the mission is over, Ryujin and Imae are heading back home to the Ministry, but find it on fire (like it had been 20 years ago). Everyone is dead save Juwon (the exorcist with pink and cyan eyes and the chocker tattoo who would give Ryujin advice). We learn Taeryung’s true identity and that he was the one who partially broke the seal 20 years ago and completely broke it now. Current King/Emperor does not trust the Ministry or exorcists, so he blames the entire incident on them, which is why Ryujin, Imae, and Juwon are in hiding. Since demons are actively wreaking havoc, the king still must now rely on the 5 great families for exorcisms, so the Moon family is hiding the 3 ministry exorcists as king cannot touch them.
Four Generals:
Geusendae- Shadow Demon (Sahon’s master the one who first proposed they break/steal the mirror)
Daesun- Dream Demon (snake boi who is infatuated with Wudo, a demon who loves humans and works with the Gyeru institute [Wudo I mean not Daesun])
Kangchul- Steel Demon (first to agree with Geusendae because she believed the mirror would be the only way for demons to survive if the Immortals left Earth; a demon lover)
Hojung- Fox Demon (betrayed demon kind and my theory is he became a new mirror to help King Chan seal himself and his “sibling” generals)
Wudo is a demon we first meet at the end of ch. 21 who introduces himself as a demon allied with the Gyeru institute. He says he loves humans which is why he lives with them and wants to fix the current never-ending winter that has fallen upon the kingdom. It seems Wudo and Daesun were lovers of sorts in the past, but when Wudo choose to interact and live with the humans, Daesun grew jealous and joined his siblings in destroying the mirror (the first time) in order to reclaim Wudo’s attention (it didn’t work as he planned).
Ryujin's Disposition:
We learn that Ryujin's body is able to hold enormous amounts of Divine Energy (which is what demons and Immortal Ones alike need to survive). This is why Sahon has attached himself to Ryujin like a leech from birth (to get Ryujin's body as a vessel for Geusendae).