Fate's Slave - Shadow Slave X Honkai Star Rail - Chapter 104: Molten Will

Meet Gu Yu—a college dropout and a talented incense maker, and at the same time, the rather stoic protagonist of this story. Despite his somewhat introverted manner, he has a tendency to make sarcastic remarks in his thoughts. One day, after saving a squirrel, a windfall (metaphorically and literally) dropped into his lap. Stumbling into the cultivation world with little help, he was not turned into Superman overnight (as he would like). Apparently, becoming a cultivator would not make your life easier, at least in the beginning.

Somewhere along the road, he ran into Jiang Xiaozhai, a young woman who’s got the brains, the beauty, and maybe one or two secrets of her own. As it turned out, the two made a perfect team—Mulder-and-Scully style. Motivated by many unanswered questions, they had been running up and down the country, getting into all kinds of trouble, and learning more of the modern cultivation world, which is by no means the same as in the ages long past…

- 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!

- Description from Novelupdates