MTL - Harry Potter and the Secret Treasures - Chapter 57 Hogwarts, millennia

A supreme expert in the Immortal World had died, and a strand of his soul returned to its original body on Earth. Tang Xiu discovered with amazement that ten thousand years passed in the Immortal World, yet only a single year passed on Earth.

Ruthlessly betrayed by his lover and trusted friends, Tang Xiu found that his soul went back to his previous body on Earth, and, despite he spent 10,000 years in the Immortal World, just a year has passed on Earth and many things have changed. Having an unsurpassed knowledge, Tang Xiu will protect his loved ones and go back to the Immortal World to take his revenge.

- Description from Novelupdates

After the nuclear warfare, massacres started to spread throughout the entire world. The order between humans completely collapses, and the strong eats while the weak gets eaten becomes the #1 rule.

Li Feng found himself in a dangerous demonic sect where he could be killed at any moment. But he was worried as he had his ultimate upgradation system.Blood Essence Pill -> Blood Origin PillTurtle Breathing Mantra -> Xuanwu's Great IsolationPhantom Spirit Fox -> Nine Tailed Celestial FoxJust like that, Li Feng was confident that he would be able to become stronger at a very fast pace and would be able to survive in this dangerous demonic sect. Not only that but as his parents were killed by some of the disciples of this demonic sect, he was also going to take his revenge on them. With his system's assistance, Li Feng was confident to reach the pinnacle of cultivation.

The World of Immortals, it is the world every mortal long for. For many, it is an eternal glory to cause a spatial distortion and enter the World of Immortals. But the vicissitude of time is simply merciless, the legends regarding immortality had long been forgotten.