MTL - Mecha and Knife - Chapter 110 ask that question

Have you ever thought about how your life would turn out at the age of 18?Well before I could even say that I was an adult to even say I was going to conquer it.The world had seemed to already be determined of what mine and the rest of humanity would be when the first Leviathans was made public to our world.

A college student was returning home after studying abroad for several years when the end of the world happened. A dragon appeared out of nowhere and attacked the plane he was in, thanks to an incredible amount of luck and his quick-thinking, he managed to survive the plane crash only to get stuck on a tropical island. A weird system took over the world and brought monsters to Earth. While nations collapsed and the world as a whole was being destroyed by ridiculous monsters, Leon was stuck on a godforsaken island with no chances of being rescued. What will happen to him? How will the world change while he is away? Will he even manage to return? The story, all names, characters, and incidents portrayed in this production are fictitious. No identification with actual persons (living or deceased), places, buildings, and products is intended or should be inferred.

A 40-year-old man suddenly dies and is reincarnated in a world devastated by zombies—but instead of becoming a hero or a survivor, he wakes up as a zombie girl.

A river song, triggered a legend of the rivers and lakes.
Tian Zun’s life motto: “My sword is the truth.”
Shen Lang’s life motto: “To serve people with morality, those who are dissatisfied are dead.”

- Description from uukanshu (translated)