I am grinding experience in another world - Chapter 5 - - Retreat

I am serious about saving people, I am professional in protecting people, and I like hunting for treasures. . . .

Emergency doctor Lu Fei was forced to travel to a small town in the United States in a parallel universe, got the rescue system, and became a legal mercenary by chance.

As a real man, you must always cut open people’s bodies to save people from danger; you must often fight and kill, and use thunderbolt methods with compassion!

- Description from novelbuddy

In his past incarnation, Lu Xuan was the youngest Celestial Lord that the universe has ever seen!
An accidental rebirth brought him back to a thousand years before, where the Earth had just begun its spiritual reawakening. When he stepped onto the way of cultivation for a second time, he swore to rewrite all injustices suffered in his past life, and defeat all enemies that dare stand in his way!
Let invincibility be his cultivation and the path he treads. In this life, it is his destiny to be invincible!

In this school fantasy story set in the distant future, creatures contaminated by pollution have overtaken the land, forcing humanity to live in isolated mobile cities called Regios. One such city named Zuellni is a self-contained school in which freshman Layfon Alseif has just enrolled. Layfon reluctantly joins the 17th Military Arts Platoon led by the third-year student Nina Antalk and embarks on a series of adventures.