I Became the Demon Lord and my Territory is an Uninhabited Island - Chapter 1

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

Lady Dawn expected to die.After casting her soul to the wind, taking a one-in-a-million chance to escape the wretched dungeons of Taegrin Caelum, the once-caged songbird of the Asclepius wishes nothing more than to find her Hearth and warn them of the coming danger. Instead, she’s found herself a shade, anchored to a young man who knows far too much—and with far less hope than she’d started with.Toren Daen, for his part, only wanted to make it home safely. Now he’s in a world taken straight from the page, questioning what is real and what is fiction, and scrambling to make something worthwhile. And with his foresight, there’s only one way that Toren can see to keep this new world safe: prevent the descent of the Legacy. But those in power will not make it easy: Nico Sever is in a league of power all on his own, and Arthur Leywin bears the burden of Fate a continent away. In this familiar-yet-not world of mana, monsters, and looming deities, any misstep along the roads of Alacrya and the High Sovereign’s Dominion could lead to a Fate worse than death.But what is death to a phoenix? With a burning secret in his mana core, knowledge of the future, and a maelstrom of fears and questions, Toren might just survive to be more than what Lady Dawn expected him to be. He might just survive to waylay the encroaching tide of death in the proxy war between raging asura clans.More than all of that, he might just live.