Arrival from Another World: Becoming Stronger Step by Step by Chewing on the Old

June 30, XX. A gray sky suddenly enveloped the earth, the sun and moon lost their luster, and the catastrophe began. Animals and plants began to mutate crazily and rapidly in uncertain directions. Humanity began to survive in the darkness. ... April 2, XX50. The first mutated restricted area appeared on the land polluted by the gray aura, and the human coalition began to fight against the mutated humanoid creatures. And discovered a giant door hundreds of meters tall. On this door is written the number '1'. In the same year, the whole nation entered a period of awakening. Various types of awakened beings began to appear, and even some hidden families also appeared one after another, just for the resources hidden behind this door. ... This novel and its characters are purely fictitious. Any similarity is purely coincidental and should not be imitated.