Gunshots, Underground Echoes

One day in the future, powerful aliens will visit the earth. Their technology far exceeds that of human civilization, and their individual strength also far exceeds that of humans. They easily destroyed all human resistance and killed all humans on the ground. Only a handful of humans who ran underground were spared and became an underground race. Compared with aliens, humans are not even in the Stone Age and can only be classified as reptiles. However, humans have never stopped resisting, and humans are not completely without opportunities. A new force has begun to emerge among humans. Who will win in the future is still unknown!