Primordial Sin System - Chapter 496 -Xegron is back

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

A man who was once called the world’s strongest agent ended up becoming a teacher after his retirement, to train a new generation of agents. After many years of training his disciples, he was killed at the age of 60 by a secret organization’s ruse and was reincarnated in another world with his memories intact. Though he was surprised by the existence of magic and the strange species in that world, he quickly adapted to his condition as a newborn and took advantage of it. He acquired special magic and gained a massive amount of strength thanks to his rigorous discipline, in order to reach his goal: Resume his career as a teacher which he left halfway through in his previous life. This is the story of a man, who, based on the memories and the experiences of his previous life, became a teacher who travels through the world with his students.

Parents dead, clan exterminated, body burned, hands mutilated, inflicted with innumerable diseases, tossed into the dump, and even the magic ring with the ghostly grandpa in it has been sabotaged. A reasonable person would roll over and die. Tian isn't that reasonable. And as it happens, neither is Grandpa Jun. A very tough kid meets a very cunning old man. And together, they will shake the heavens. What to expect:-1 chapter a day M-F. Volume 1 is already complete.-2k words per chapter (aprox, some run long) with a longer first chapter.-No Harem-Earned power growth-An MC who isn't a goodie two shoes OR an edge-lord psychopath-A power system based on actual Daoism -Sects, giant monsters, natural treasures, flying swords, spells, talismans, secret arts, and a gentle sprinkling of young masters whose face need rearranging.