Starting with Check-In Sacred Body of the Ancients - Chapter 207: The Agreement is Made, Obtaining the God-Swallowing Demonic Art and the Netherworld Continent’s Origin

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

Yi Zaha. The crazy demon crazy for martial arts. While he was running away after stealing the heavenly pearl of the Demon Cult Leader, he fell off a cliff. After thinking that everything was over, he opened his eyes to see that he had returned back to when he was a waiter… And he is being beat up for something that he didn’t do. The crazy demon who returned to the beginning of his days as a waiter! Will he go crazy again, or will he drive his enemies crazy?

A life filled with regrets.Once he realized his faults and decided to lead a new life, it was too late.His family was already gone.He had borne through each day with pure rage.Finally at the end of his misery, his wish reached the heavens—an unforgiven one.He goes against fate to raise his sword.

In the city of Graheel, a small antique shop sits quietly mixed in with all the other shops. Its unassuming appearance is easily overlooked by many. However, this store and its owner has a terrible secret. A devil lives in that building. The owner of the store, John Li, an enigmatic figure whose origins and intentions are unknown. The desperate from around the world, often unknowingly, come to him in search of salvation.A red witch thinks the owner is an ancient creature, a white fox calls him a wizard of eld, a warrior believes him to be a spirit, and a holy woman declares him a god. This mysterious individual and his customers would stand at the center of a strange series of events. From the store owner John's perspective, he has no idea what's going on. He really was just an unlucky dude that got caught up in some crazy stuff.