Elf Tensei Kara no Cheat Kenkoku-ki - Chapter 12Book 3: -3: The Gates of Hell

Oscar, a destitute young boy, died in a tragic accident and was reborn in the forgotten realm. As a member of the lowly Birch tribe, his solace comes from the fragments of a guardian's spirit, residing in his soul. After the decimation of his family in the hands of a powerful race known as the dreads, he embarked on the part of revenge, leading him to the path of transcendence.

Zero, a 35-year-old mercenary, after being betrayed by one of his teammates who told his enemy about him. He chooses suicide so that he can kill his enemy and his traitor teammate. After that, he was reincarnated into the world of magic, in the body of an 18-year-old teenager with the same name as him. However, his body does not have mana or the talent for magic. But with the help of the cultivation system, he has unrivaled power in the world and has a harem of beautiful wives.

The end of all worlds approaches.

The Demon King Order harvests lives from all manners of living beings.

Within this darkness full of despair,
A single person escaped from space-time, returned to before the world collapsed, determined to change the fate of the past.

But as time pass, he gradually finds out that the Apocalypse isn’t quite as simple as he thinks…

- Description from novelupdates

A story about a traveler who crossed into a parallel universe, relying on his Proficiency ability to continuously grind experience and become stronger.