The world of Evo was once peaceful, until a battle between Gods and took place therefore weakening the seal on the demons.
There were now able to open gate leading to Evo,as the inhabitants of the world saw the gates the were scared and left that path of the world.
After sometime the yellow gate broke and numerous demons invaded Evo. All the weapon present weren't able to kill the demons and the demons could also regenerate any injury inflicted on them. That was how it started and many people died until a man was able to wield the energy the demons use which is now called chaos energy, to summon a weapon able to exorcise the demons and the humans started pushing back.Some brave people entered the gates to kill the demons and breakthrough to higher levels.