Regression Is Too Much - Chapter 39: Rapid Changes on Earth (4)

A social worker father and his adult daughter crash land on a desert full of crystal plants and little else. The city walls of Ar'Kendrithyst rise in the distance, but as the pair hike closer they see those walls are more like mountains, and the mega-metropolis is long dead. Luckily, the adventuring city of Spur is alive and green and hospitable, and well outside of Ar’Kendrithyst’s shadow.Follow Erick Flatt as he tries to make a nice life with new friends in a new home with his daughter at his side, but this land is rarely as kind as its people, and Erick will need to change if he wants to live the life he wishes to live. What to expect:Slow burn storyline, worldbuilding, father-daughter relationship, Erick is the MC, Jane is the side character, slice of life, numbers in blue boxes but also high fantasy, trying to understand magic, creating new magic, living the easy life but forced into dealing with problems, problems becoming very large, massive changes, traumatizing content, and most of all: character growth.

He rose from abjection and achieved eternity in glory.
He embraced the prettiest beauties and killed the strongest opponents.
He was able to shift the clouds into rain and cover the sky with one hand.
He could overrun the entire world and go anywhere as he pleased.
He pacified wars and held the world in awe.
He was matchless in the world.
However, his hair turned white overnight for his beloved woman and he was on the verge of death.
He was surrounded by enemies who were trying to take his life.
He struggled his way to become mighty and fought for everything he cherished.
For this age, he was the only king of the Dark World.
His name was a byword for might.
As a man living in the world, his only ideal was to pursue brilliance.

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

He became a teacher at the best magic academy in the empire.
….For being mistaken for someone else.