MTL - God Level Demon - Chapter 2923 Sage gathering

Killed by a Sage Emperor and reborn as his 13 year old self, Nie Li was given a second chance at life. A second chance to change everything and save his loved ones and his beloved city. He shall once again battle with the Sage Emperor to avenge his death and those of his beloved . With the vast knowledge of hundred years of life he accumulated in his previous life, wielding the strongest demon spirits, he shall reach the pinnacle of Martial Arts.

Wen Zhixing has transmigrated into the world of cultivation and has been unexpectedly abducted to the Wondrous Palace, where is full of infamous female cultivators. However, with his Immortality System, Wen Zhixing discovers that he could see their “Fortune Fragments” and take advantage of these Fragments by consuming his lifespan.[ Acquire the constitution: Revival of the Withered Tree.][Revival of the Withered Tree: Blazing Gold Quality. Can rejuvenate a withered body. Each time the body enters a withered state, it will undergo nirvana. After nine nirvanas, it will shed its mortal form.]...

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

The world had changed when the System arrived, alongside the Cataclysm that filled the world with monsters. The technology was gone, replaced by classes and skills that allowed the people to fight back. When Devon ended up as a Blacksmith, a class that didn’t grant Intelligence, he had to face the reality, that his old career that he loved - mathematical sociologist - was over. Instead, he had ended up as yet another discarded member of the production class, overshadowed by the existence of the System Shops to the point of total marginalization. But, what if all he needed was to reapply his scientific thinking to the System...