MTL - Simulation: Starting From Strange Creatures - Chapter 176 Spit it out

When he did not know her true identity, he treated her very badly, he disliked her too much, she was not elegant enough, she was in the way...Only later did he realize that the woman was his legal wife! He repented, tried to recover her feelings, but she was determined to divorce him.

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.

On the surface, he is the aloof and standoffish patriot whose sole purpose is to serve the nation. On the darker side, he is an invincible, powerful and mysterious man.

When Arran decides to become a mage, he quickly discovers that magic can be more dangerous than he had ever imagined. Soon, he finds himself hunted for powers he never knew he had.