MTL - Guardian (Bu Hui Xia Qi) - Chapter 43 Division by subject

Mu Zhiyan, after being transmigrated a millennium (1000 yrs) into the future, discovered that he was raised by his adoptive parents as a tool for them to access the heritage his (dead) biological parents left behind. When he was at a loss for what to do next, he discovered that his body hosted an additional
pharmaceutical system.

For a chance to return to his era of Earth, Mu Zhiyan decided to practice and practice; he must train the system to full level as soon as possible.

However, reality gave him a slap in the face. The world is dangerous and dreadful, making Mu Zhiyan recall his mother’s words of holding a thick thigh, resulting in him locking his eyes on a cool general…

So the rumored mysterious Mu Master faced General Han with a serious face: “I allow you to follow me, General Han.”

General Han: “…”

- 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.