How Does The Novel Secret Connect To Demon Slayer'S Lore?

When Mizuko slipped into the other world, she landed in the arms of a mischievous demon prince, Kenshi. New to the world, she didn't know he was a demon as he looked to her like he was a decent person. Because Kenshi helped her first, Mizuko decided to ask him for help in finding a way home while she fulfills the dead mage's request in relaying the message to the King. But no demon in Souzou helps unless they get something in exchange. A promise, it is what Kenshi wants the most.

After 15 years being tortured by the Assassin's Guild, Aria and Sebastion find themselves with another group of people who are determined to bring down the tyrannical rule of the Assassin Guild. With each and every passing day more secrets are unlocked and the people they work for are not who they say they are. So what is Master's Secret?

He died killing the Demon King. He woke up sixty years too early. Now the monster is a young man. And he is running out of reasons to stay away. --- Lysan Dusk was the hero who saved humanity. He killed the Demon King, ended the war, and delivered the world from suffering, and his reward was betrayal. He wakes up in a young student's body in a dormitory room of a magical academy, and the calender shows that the date sixty years before he was born. The world outside hasn't broken yet. The war hasn't happened. Lysan's plan is to keep it that way by staying completely out of it. Fail his combat exams, spend whatever borrowed time he has left, living a quiet life, where nothing requires him to be a hero. The man who will become the Demon King, the most feared monster in history is still young and beautiful, with pale grey eyes that find Lysan across every crowded room like he is the only person worth seeing. Lysan knows what those eyes will become. He has looked into them across battlefields, spent a lifetime seeing them in nightmares. He never expected it to feel like this up close. Roman is everything Lysan was warned about — magnetic, dangerous, impossible to ignore. Everyone except Lysan, refuses to be charmed, refuses to feel anything at all. But now, he is failing spectacularly at them because Roman keeps finding him. Keeps watching him and making Lysan's carefully rebuilt walls feel like paper. Lysan knows the ending. But for the first time in two lifetimes, he is wondering if the ending can change. If the monster can be loved instead of killed. If staying is braver than running.

"This is your new sister," they said. "Protect her," they said. Not love her. Not obsess over. Not need the lost and abandoned orphan with no where else to go with every fiber of my being. Just protect the new messenger of the old gods, with all that I am..... Forbidden love in a lost world of fairies, shifters, and Shin.

The Demon King’s Bride The entire kingdom fears him. With white hair, piercing blue eyes, and a heart sealed by cruelty, King Edrion is known as the Demon King—a ruler who accepts betrothed brides… only to turn them into concubines and discard them without mercy. When a young noble lady is promised to the king, her fate seems sealed. But she refuses to give up her freedom—or the man she secretly loves: a guard from her own household. Desperate, they devise an unthinkable plan—to have a poor girl, identical to the noble, take her place as the royal bride. The girl agrees to assume a life that is not hers, believing she will become nothing more than another forgotten concubine in the shadow of the throne. What no one expected… is that the king would choose her. Now destined to become queen to the most feared man in the kingdom, trapped in a lie that could cost her life, she must survive the court, a forbidden desire, and a king who was never meant to look at her the way he does. Because the Demon King does not love. But when he chooses… he neither forgives nor lets go.

Serra is a normal senior high school student who works really hard every night and weekend to pay off her parents' debts from loan sharks. But when she couldn't keep up with payments anymore, she decided to end her life. Surprisingly, she woke up in a different light-- in another world. What's more shocking was when she is addressed by one of the people as the demon king's bride.