MTL - Duel Monsters of Global Cards - Chapter 153 Devil's Call

Freshly turned eighteen, John Newman, a helpless nerd, suddenly gets video game abilities granted to him. A mysterious higher power, a secret Abyss of magic beneath the surface of the normal world, mages, martial artists, eroticism, tragedy and a harem of hot girls awaits.

This is a very interesting thing. It is obviously dim and black, but it can emit a golden light, which makes people deeply fascinated by it…

- Description from novelbuddy

Empires rise and fall on the Yulan Continent. Saints, immortal beings of unimaginable power, battle using spells and swords, leaving swathes of destruction in their wake. Magical beasts rule the mountains, where the brave – or the foolish – go to test their strength. Even the mighty can fall, feasted on by those stronger. The strong live like royalty; the weak strive to survive another day.

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