Howl No Ugoku Shiro

Sinopsis

In a world where hunters, humans who possess magical abilities, must battle deadly monsters to protect the human race from certain annihilation, a notoriously weak hunter named Sung Jinwoo finds himself in a seemingly endless struggle for survival.

After narrowly surviving an overwhelmingly powerful double dungeon that nearly wipes out his entire party, a mysterious program called the System chooses him as its sole player and in turn, gives him the extremely rare ability to level up in strength, possibly beyond any known limits.