The three large-scale 'Apocalypses' that nearly wiped out humans were composed of three parts. Firstly, it was the Original Sin of Calamity that existed for only half an hour. Secondly, the Seven Deadly Sins would wreak havoc for three days. Thirdly, all sorts of natural disasters like earthquakes, tsunamis, and volcanic eruptions would constantly occur.
The Original Sin of Calamity was no doubt the strongest existence. Although it was unknown why the Original Sin of Calamity would only exist for half an hour, it would be able to kill nearly all the strongest people in the human world in the thirty minutes. Ten thousand years ago, the pixie species which Kali was from had all its strongest figures annihilated by the Original Sin of Calamity, including her mother and grandmother.
