What Book I Should Pick Up If I Loved Demon Slayer?

A normal girl just as usual working every day. This changed when she met a demon. She made a contract with the demon to help her. She just want to use her demon, but she find that she can't help fall in love with the Demon

A 25 years old boy named John is suddenly shot by his friend, which results in his death, but is reincarnated again as the new Demon King. Unfortunately, he agains dies in a battle. This time also he is reincarnated but as a human. Follow Vis' adventure as he gets revenge, becomes a demon and makes his own harem.

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.

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.

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.

Arianna had not planned on using magic to summon anything, she just wanted to get out of an arranged marriage. She was told of the ancient magic of summoning a guardian but instead she had summoned a demon—the demon king himself. But what would he ask in return for his loyalty to this princess?