Lucaon is a royal blood, a survivor from becoming a zero. (where royal bloods became unwillingly taken out of their will to destruction : kill)
There's two ways to corrupt a core (the source of the royal blood's power) first is when they became mentally unstable and shock. Second, is, if you drank a vs solution (a poison that can corrupt your core).
The only cure for a corruption are 1) if you are mentally shocked (Like Lucaon), Ryan can save you and give some of his powers to save you. But Lucaon still has some left mark of becoming a Zero. 2) If the offender is still alive, they can heal you and redo the poison's effect.
There's an organization called Intron, that controls people and zero. They have a sample of VS Solution. They also held accountable for Lucaon's parents death.
Lucaon's parents were trying to search a cure to the vs solution or for those people becoming a Zero. When the Intron knew about this, they were poisoned. Lucaon, his parents and Ryan were having a meal, and a wine was served. All of them, except Lucaon, drank the wine. Some days after that, while Lucaon was out of their home (he was a hunter, they were saving a child called Kyon from a zero attack), he came back, to see that his mother and father became a zero and killed eo.
Lucaon has a friend named Sihan (a royal blood, born servant, and a hunter, adopted by ryan) who has a servant and a lover called Karis. They were helping Lucaon to solve the case and find out the killer. It turns out that the offender, "commited suicide" and that's the reason why they cannot cure Lucaon's parents.
Kyon, on the other hand, grew up and was looking for a job. Someone suggested to him to become a Royal Blood's Servant because the pay is well. He tried to work there and he became close to the master, Lucaon. Lucaon came to know that Kyon likes him and tries to rape him. After that, they have been having sex and it has been come an issue within servants in the Selvior Mansion.
One day, a zero attack has invaded through the Selvior's mansion and resulted to Kyon remembering his past. He was Edwin's (Intron) spy. (The intention was to go inside Selvior Mansion and make Lucaon drink the VS Solution. Also resulted to erasing Kyon's memories and past so that Cecil wont read onto his head) After that attack, servants, except Kyon, decided to quit because they were scared if it happens again.
Ryan, came up with a friend, Cecil (a royal blood hunter) to ask for a help and gather 10 hunters to look after Lucaon.
Kyon, remembers his past, and about Edwin. Now, he knows he his a threat to Lucaon. He decided to tell it to Ryan and they made him unconscious and Cecil checked that he is really telling the truth. Ryan and Cecil came to an arguments and proposition to either let go of Kyon or make him to stay. But, Lucaon doesn't want him to quit, he even doesn't know the reason why.
One day, Lucaon and Kyon decided to visit Sihan on their mansion and to sleep over. Kyon kept insisting to eat together with Lucaon and the others. But, Lucaon doesnt want to eat. One morning, he prepares a breakfast for him and for lucaon but he cant seem to know what to prepare. Cristoph (a mixed blood servant from Ryan and Sihan) was there with him and suggested to make a tea. Cristoph prepares it and gave it to Kyon, so that he'll be the one to personally give it to Lucaon. And, Lucaon did drink the tea.
Going back back to Lucaon Selvior Mansion, Cecil was there amd wanted to talk with Lucaon about Kyon. She sensed there's something wrong with his core and told him it's corrupted. They have suspected Kyon, because he constantly wants to eat with Lucaon, however, it turns out that the core doesn't do anything when Kyon is near Lucaon. So it was not him.
Ryan and others knew about this, and Ryan even wants to kill Kyon because he is a threat to Kyon. Cecil decided to tell Lucaon about the situation, and was mad. That's the reason why Kyon kept wanting to quit as a servant but he wont tell him.
in the end, they decided to go to Edwin. A servant named Emma, located Edwin's address. Ryan and Kyon (because Kyon will probably be familiarized at Edwin's mansion) went there. And they found out that, Cristoph was the culprit.
Kyon found Cristoph documents at a book of Selvior founded at the mansion. And, Ryan found about it when Edwin said "Look at me, cant you tell who it is?" (Cristoph's and Edwin's eyes have the same color) .
The culprit who mixed a VS Solution on Lucaon's tea, and Lucaon's parents' was Cristoph and he was ordered by the Intron. 1) Cristoph used a servant and make him the offender instead of himself, mixed a VS Solution at the wine, that Lucaon's parents and Ryan drunk. After that, Cristoph killed the offender so that Lucaon's parents wont be cured.
2) Cristoph offered preparing a tea For lucaon, in which he also put VS Solution on it himself, that's make him the offender.
When Kyon returned at their mansion, together with Cecil. They confronted Cristoph and they cured Lucaon.
However, they also knew that Ryan drunk a vs solution on that wine that night with Lucaon's parents. They never knew someone like him can die too. He asks a favor from Cecil that he wants her to erase Cristoph's memory of Ryan. Because of Cristoph, Ryan will die. (kasi nga pinatay nya ung offender that night) And Ryan think Cristoph will be devastated once he knew.
So , napawalang bisa ung kasalanan ni Cristoph, he doesnt remeber a thing. All of Ryan's remains were deleted and erased at Sihan's mansion. They don't mention Ryan anymore esp when Cristoph is around. And Ryan died peacefully.
kyon and lucaon relationship changed into a special one. They already cut off the master and servant, and Lucaon gave Kyon the mark as like they were married.
A flashback:
Ryan was the one who invented the VS Solution. But, word has spread out and it was even sold in black markets. Resulting to a second son of the Selvior family to turn into a Zero. A friend of Ryan suggested him to make an antidote but it's impossible. So he wants Ryan to be a leader of hunters. That's why he was close to Selvior family, because they'll be an instrument to finding a cure. The reason why he adopted Lucaon like a son, and also Sihan.
Royal Servant