The Great Core's Paradox - Chapter 18: A Slow Death

The hearse with the weird odor slowed to a stop before the entrance. The sound of pebbles could be heard bouncing on the ceiling. There were footsteps coming from the corridor, and there seemed to be someone sawing next door. The door knob to the room rattled slightly, and the faucet in the bathroom kept dripping even though it had been screwed shut. There was a rubber ball that rolled on its own underneath the bed. Wet footsteps started to surface one after another on the floor.
At 3 am, Chen Ge held a cleaver in his hand as he hid beside the room heater. The call he was trying to make was finally answered. “Landlord, is this what you meant by ‘the house can be a little crowded at night’‽”

- 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.