Apocalyptic Demon Hunt

Crazy thunderstorms, pouring radiation rain, scorching days, nuclear dust storms, earth-shaking earthquakes... Everything has nothing to do with Loya, who is trapped on the fifth floor of a collapsed building. Day after day, year after year, he uses his index finger to control a fleshy tentacle drilled into the ground from a water pipe to capture passing creatures, absorb the nutrients of the creatures to maintain life, evolve his body, and wait to see the light of day again...! What will it look like outside? Can humans still exist amid the ravages of hyper-evolving creatures?