I Am Not a Weapon King, I Am a Civilization Designer

A military engineer traveled to the world of high martial arts and found that the strong men here were practicing hard on their bodies and competing for their talents. He silently took out the blueprints, from exoskeletons to individual mechas, from psychic rifles to interstellar battleships... When the alien gods invaded, the world's strongest men were in despair. Behind him, the torrent of steel blocked the sky and the sun. He calmly ordered into the communicator: "Civilized fleet, saturation firepower coverage. Tell them that times have changed."