I Possessed a Demon Sovereign - Chapter 741 - : 739. The Tranquility Before the Storm

Violet skies, a world undergoing massive changes, a deficient moon, interlinking voids…
When the world experienced a cataclysmic event,the majority of living things ceased to exist. Although humanity survived by hiding in the last safe zones, humans had to face mutated dire beasts and colossal source beasts that could break through the space barrier and enter the earth at any second.
Luo Yunyang, a young man who grew up in those calamitous times, obtained an attribute regulator and set out to walk the path of supremacy!

- Description from novelupdates

After 140 years that gates and dungeons appeared on Earth and a system allowed humans to use special abilities, Matthew an 18 years old who just got out of high school will seek adventure inside those perilous places. However, instead of being able to select his own class as he progress the levels, destiny has another plan for him.

Time flies quickly; may you enjoy a cup of drink.I know not the height of the green mountain, nor the depth of the earth.Only watching as the seasons change, that it took people's lives.

A man who was once called the world strongest agent ended up becoming a teacher after his retirement to train the new generation of agents. After many years of training his disciples, he is killed at the age of 60 by the ploy of a secret organization and was reincarnated in another world with all his past memories.Though he was surprised by the magic and the strange species of that world, he adapted very fast 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 tight 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 new students.