Iron Blooded - Thirty Eight: Tides of War

He is a young man without a spirit root. It is believed that this denies him the chance at cultivation. However, a mysterious lady imparts a Supreme Demon Classic to him and from then on, he starts his path of cultivation.
He undergoes a total transformation to emerge as the most fearsome and powerful fiendish demon in his era, that even immortals and fiends are fearful of him, and saints are at his beck and call.
Mastering the Supreme Demon Classic is the turning point in his life. He is able to unleash his immense and divine power from within, illuminating the entire universe!

- Description from Novelupdates

SLASH!(So this is death?!!)I, Elysia, found myself dead before even reaching the Demon King's lair, and our Hero Party was completely annihilated.And this was done by none other than a fellow human—my former classmate.He had been mostly invisible during our time at the academy, but then he started committing one crime after another until he became a lackey of the Demon King.Who would have thought that the strongest party of humanity would be wiped out by humanity’s traitors?(If I could go back to the past, I swear I will kill you!)Just when I thought I could finally pass on, I opened my eyes.Five years back, when I first enrolled at Arcadia Academy.And there he was, the traitorous bastard of humanity...****“Huh? Where am I?”One day, I opened my eyes to find myself in an unfamiliar place and came to realize this was the world within the novel Savior's Dawn that I had read.Everything seemed to be proceeding the same as in the novel—except for one thing.The main heroine is glaring at me as though she wants to kill me.Could I survive with the main heroine after my life?

A dark soul, damaged by his past An angel forced to be his mistress. Can anything go right? Would they ever be able to fall in love? Will she be able to see past his darkness? Will he be able to protect her when danger comes knocking? Find out in this book... An Excerpt*

''You know what you are getting into, right?'' He asked, crossing his legs, he raised a brow;

Tiana's lips slanted and her eyes narrowed at him;

''As long as you pay me, I'll do whatever you want. '' Nicklaus was amazed by her sudden audaciousness;

but he was sure she was just trying to seem bold, He knew her, she was just a weak, trembling soul, and she was trying so hard to mask it;

A smirk appeared on his lips as a thought came into his mind; ''Whatever I want? ''

He asked again and Tiana replied immediately without a second thought;

''Yes, Mr. Nicklaus, whatever you want. ''

''Alright then, I want you to strip yourself and go lie down on the bed. ''

He did not have any thought of touching her; he just wanted to see her reaction. But what Tiana did next shocked him.

What happens when a man gets transported into a foreign world filled with magic?