Thousands of years ago, the sky opened and the abyss descended.
Countless strange beasts emerge from the abyss. They feed on humans, using emotions as energy and fear as nutrients.
Ninety percent of human civilization was destroyed, and the survivors hid in the "Walled City" - a city surrounded by huge energy walls.
But the boundary wall is not eternal, the alien beasts continue to evolve, and human power... Is drying up.
Even more desperate is:
Among humans, there will be "Abyssalizers".
When they are emotionally agitated, fearful, angry or sad, their bodies will partially transform into beasts, their strength will surge, but they will also gradually lose their humanity.
Abyssalizers are regarded as monsters and are ostracized and hunted by humans...
But they are also the only hope against the alien beasts.
