MTL - I Bound Aizen - Chapter 91

Lassen, a young man who has failed at everything in his life, has had enough. Disillusioned with the world, he decides to end it all. But instead of dying, he wakes up in a parallel world, armed with a strange system that can accomplish anything he desires. Trapped in his room, reading novels and savoring every page, he has no intention of participating in the fast-paced world outside.Yet, despite his desire for peace, the world changes every time he makes an appearance. Everyone treats him like a genius, a being capable of disrupting the very fabric of reality, without lifting a finger. A powerful system, a new life, and a world that adapts to him: why complicate things when you can have everything without effort?The Genius System tells the story of a man who, although having everything to change the world, prefers to watch it evolve from the comfort of his room, through the pages of his books.

Vainqueur Knightsbane is your average dragon: a giant, fire-breathing lizard who loves to take naps on his golden hoard, kidnap princesses for fun, and make the life of adventurers miserable. Vainqueur's only pleasure in life is to watch his treasure get bigger, one coin at a time.

So when a would-be thief turned unwilling minion tells him about "classes," "levels," and "quests," Vainqueur wonders if maybe, just maybe, he should consider a career change.

After all, why bother hunting monsters for free when you can get paid for it?

To pass as an imperial concubine, one must be professional.

Actually, the profession of an imperial concubine is pretty good. The emperor will accompany you in eating and drinking, and even pay you for it. What’s not good about that?

- Description from Novelupdates

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!