He is the rightful heir to the Kingdom. The crown and the throne are snatched away from him due to a split-second unjust villainy plotted by his own brother, whom he trusted with his whole life. Kai is the bastard son of the Queen, who has no prospects of ever claiming the throne so long the King and his Prince live. Sehun is the young Crown Prince of the Kingdom of Havegnia, whose his entire fate changes when his half-brother executes an overnight coup to assert power over the throne. He crowns himself as the King, the supreme ruler of Havegnia at the age of 17 upon assassinating the King in his sleep in cold blood and locking the Queen and Sehun away. With great sacrifice, the Queen manages to liberate the 9-year-old Sehun and implores him to run as far away and as fast as he can.
That was the last time Sehun had seen the castle he was born in and his beloved mother. Taken in by a group of Vagabond Slayers, Sehun trains for years to become the most notorious assassin, with only one incentive—return to Havegnia to reclaim his throne as the rightful heir, save his mother and kill the traitor he once called his brother. With the fire for vengeance burning within him, he bends over backwards, doing his damnedest to become an adroit assassin and upon reaching the age of 18, he returns to Havegnia.
Everything goes according to plan until he finds out the King, his half-brother, the man who preens on his glorious winning and procurement, is a man who is almost indestructible. If there's anyone who can dauntlessly stand against Sehun, it's Kai alone.
As the bastard of the Queen, Kai knows he has no chance of becoming the King with Sehun and his father in the way. He's a ruthless King who has very little mercy for the ones below him. Married to the beautiful Princess of Triyan, Kai has more power than any other King in the world. Even after securing his position on the throne, it isn't enough for him. He wants more. He wants to remain King forever, especially since he knows the young Prince still lives.
On the mystical land, he has the opportunity to gain immortality, but only with great cost. All he needs to do is procure the Six Spirabiliz: consume the Fruit of Cael from the land of Jehovah, bathe in the Lake of Aevitas, find the Ring of Iugis, hold the heart of a lion, consume the tear of a Nympharum, and the last Spirabiliz will uncover itself. All that he needs now is an adept bulwark to accompany him to find the Six Spirabiliz and the Vagabond Slayer falls right into his trap. In return, Kai is willing to offer the assassin his life and freedom. Only after enslaving the assassin as his personal thrall and wrecking every inch of the boy's body.
Without even the knowledge of Sehun being the Crown Prince, Kai embarks on a murderous journey with him.
READ THE WARNING AND DON'T CONTINUE IF ANY OF IT TRIGGERS YOU!
WARNING: Smut, rough smut, bondage, dub/non-con, incest, kinks. Violence (!!!) Ruthless, cruel Kai. Ruthless, cruel Sehun. Purely fictional (duh). Yes, Kai is married, so expect cheating.