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Entertainment, Balance, Gameplay, and Story.
The four basic requirements for a videogame.
And even as Arcadia is actually a real world, these are still necessary.
Why? Because the world itself seems to be maintained by the power of the System, which has transformed it all into a videogame-like world.
From what I've learned from that dungeon, it appears the past had no such game-like powers. People seemed to cultivate Mana and Ki into their bodies, and they mostly used martial arts and spells.
They had no levels at all either! No Skills, and no items. There were things called Relics, which was the closest to equipment, but they worked using divine power.
However, this world was much different than what it is now. Events, Quests, Items, Skills, Levels, Players, everything in between, such things did not exist.
