MTL - Correct Posture For Redemption - Chapter 49 ,Small dogs

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

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.

There is no master god, no system, no exchange, and some are just source codes that are fused in the mind to open up the world, not to be forced or suppressed, but to constantly go through in order to become powerful Look at my infinitely powerful source code …

- Description from uukanshu

In the year 2220, a radiation source in the Pacific Ocean, tens of thousands of times stronger than a nuclear bomb has begun mutating exposed creatures into horrific monsters thousands of meters long. Mankind’s only hope was nuclear weapons, which only made matters worse. The combination of the natural radiation and nuclear radiation released an incurable and highly infectious virus, turning the 90% of the world’s population into violent zombies in mere weeks.