I Have the Most Awesome Craftsman System in the Universe

In AD 2679, giant monsters suddenly appeared, causing the world's population to decline. Countries have also built walls one after another, which has slowly improved the economies of various countries. In the intervening years, giant monsters began to appear but they were all smaller monsters. Our male protagonist also encountered this small monster, but at the moment when the male protagonist was about to be shot to death by the small monster. With a ding, the system appeared...