So, for those who don't know, <<The Gamer>> is a Korean graphic novel focusing around a teenager by the name of Han Jae-Han(though the spelling does tend to vary between translators) waking up to discover the logic and physics of an RPG game being applied around him. Things only get crazier from there, when he discovers there are others - "ability users," as they're apparently called - around him, creating separated realities where they can do as they please with unique powers without consequences. These realities eventually take to the names "illusion barrier" and "instant dungeon (when there are monsters involved.)"

The basic gist on "ability users" is, there are natural and trained ones.

Natural ability users gain abilities relating to events in their life. Jae-Han played video games most of his life, and the resulting ability was fine-tuned accordingly. It was later discovered that it was the top tier of ability user power, because it starts weak, but can grow more powerful...With no upper limit. Others usually just start with a decent amount of power.

Trained ability users, however, are not naturally attuned to getting these abilities. Instead, they, quite obviously, train and gain these abilities. The Chunbumoon clan is the chief "trained ability user" spot in Korea.

Both can create illusion barriers, and learn various abilities over time. They are organized through a system of "tiers," the top tier being "natural" ability users who start weak but grow more powerful over time, and those who passively warp reality. The lucky sunuvagun, Han Jae-Han, managed to get both wrapped into one by playing video games for most of his life.